Since I updated my MacBook Air 10/26/19, I keep getting a popup that reads ""update" will damage your computer. You should move it to the trash". When I click Move to Trash, my computer continues to load as usual but it reloads the popup each time

Here you go: Back up your files with Time Machine on Mac - Apple Support.

I think all you need to do is select "Back Up Automatically" which will at least enable you to recover using Local Snapshots, however, since I don't have any Macs that have never used Time Machine I am unable to provide absolute assurance that it will.

The following excerpt from About Time Machine local snapshots on Mac (emphasis added) seems to indicate that's all you need to do though:

"Local snapshots are captured only on disks using Apple File System (APFS) when Back Up Automatically is selected in Time Machine preferences. On your Mac, choose Apple menu  > System Preferences, then click Time Machine."

It's a shame a lot of Mac users (based on the reports from this site) don't perform that simple action.

I could not locate "users and groups"

It's in System Preferences. There may be a Login Item associated with that program, in your User Account: Open items automatically when you log in on Mac - Apple Support. If the nag is gone though it's probably not present. You're probably all set.

First, ensure you have a reliable backup of your Mac, in case something should go wrong with continued troubleshooting. To learn how to do that, please read Back up your Mac with Time Machine.

• A backup is a fundamental prerequisite regardless of whatever method you may choose uninstall adware, and would apply even if your Mac were running perfectly well. Do not overlook this fundamental requirement. It's important.

Next: This step is optional, but will preclude any related inability to use your Mac due to the effects of that recurring process. Restart in "Safe Mode", and log in: Use safe mode to isolate issues with your Mac. Starting in Safe Mode takes longer than usual so let it finish. The resource-demanding process will not appear while you are using your Mac in that mode.

The following files and / or folders need to be deleted while using your Mac in "Safe Mode":

~/Library/LaunchAgents:

Drag that file to the Trash. You may be asked to authenticate. Confirm it is no longer present in that folder. Leave all the others alone for now.

Nothing needs to be deleted from the other two folders.

Next: open Safari and select the Safari menu > Preferences... > Extensions. If you see any Extensions that you do not recognize or understand, simply click the Uninstall button and they will be gone. No Safari Extensions are required for normal operation. Then, select the General pane and review your Homepage selection. Repeat those equivalent actions for any other browser you may use (Firefox for example).

There may also be an app associated with that process in your Mac's Applications folder. Open it and examine its contents. Any unwanted or mysterious app icons should be obvious to you, but again please don't remove anything if you are uncertain—ask first. Identify any suspicious apps by name, or post another screenshot.

Next: In an abundance of caution, examine System Preferences > Extensions. Determine if there are any Extensions that may have been installed without your knowledge. Ask if you're uncertain.

While you're there, check for the presence of any Profiles. Profiles are installed by organizations with a need to manage Macs deployed in institutional corporate or educational environments (for example), but have also been exploited by adware creators and similar malcontents. Unless your Mac is used in that sort of managerial setting, no Profiles pane should appear in System Preferences.

Remaining within System Preferences, open Users & Groups. Select your User Account's Login Items. You may or may not find those Applications in its list. If you do, select them then click the [—] (minus) button to remove them from Login Items.

• Merely selecting the "hide" checkbox does nothing but launch the app without it being visible. To remove it from Login Items requires using the [—] (minus) button.

You can then restart your Mac and log in as usual. Confirm that popup stops appearing. At your option, you may also wish to inspect Activity Monitor for anything that may be related to it (for example, a process bearing the identical name as that "xxx will damage your computer" dialog would be suspicious), and that your Mac's operation generally returns to normal.

Next: if you want to eradicate all remaining adware remnants post a screenshot of the following folder, in the same manner as you did earlier:

~/Library/Application Support

It is normal for that folder to contain many items, but anything associated with the above adware will bear identical names ("Vidplayer" for example). If you find a folder or folders bearing that name, drag them to the Trash. Without the files you already removed or the reintroduction of similar malware, they can do nothing but occupy space. These can be removed if you wish, but again don't remove anything if you are uncertain.

Finally: If any of the above actions result in abnormal operation or if something else stops working, the easiest way to recover would be to restore the Time Machine backup you created as a prerequisite, so the importance of that fundamental step cannot be overemphasized.

Whatever it is is probably being loaded as a User Launch Agent, System Launch Agent, or a Login Item.

First things first: Navigate to the following folder, and post its contents in a screenshot:

~/Library/LaunchAgents

To open that folder, copy the entire line above and paste it in the Finder's Go menu > Go to Folder... field. Make it look like this:

... and click the Go button.

A Finder window will open. Take a screenshot showing all that folder's contents, and post it in a reply. To learn how to do that please read the Appendix in the following User Tip: Writing an effective Apple Support Communities question.

Usually, there is nothing in that folder so don't be surprised to find it empty. The reason for starting with that folder is to eliminate other potential causes before proceeding with steps that will identify and eradicate whatever is affecting that Mac.

There will be additional instructions to follow and this is just the first step.

Thanks. In the same manner as the above, open the following folder:

/Library/LaunchDaemons

To open that folder, copy and paste it in the Finder's Go menu > Go to Folder... field. It should look like this:

Once again ensure all its files and their names are readable, take a screenshot, and post it.

Then, repeat that exercise with the following folder:

/Library/LaunchAgents

Notice its pathname is different than the other two.

In the end, you will have captured and posted the contents of the following three separate folders:

~/Library/LaunchAgents

/Library/LaunchDaemons

/Library/LaunchAgents

Please be sure to include or otherwise indicate the name of the folder that corresponds to each screenshot, so that you and I can keep track of which ones they are.

The adware (assuming that's what it is, which I believe to be the case) was certainly present prior to upgrading macOS to Catalina. Its date confirms that fact. The only reason you became aware of it is that Catalina added additional precautions that resulted in the appearance of that dialog.

In other words nothing has changed. Catalina is simply making you aware of it, and you should proceed on the basis of that knowledge.

The Time Machine backup is fundamental. Even if your Mac were working perfectly, everyone should be using Time Machine. The feature is free. All you need to do is turn it on. If you are 100% confident that you would not lose any work in the (unrelated) event your Mac were to be lost, stolen, or simply refused to start up one day, then you're ok.

Also bear in mind my instructions are conservative; arguably, overly so. I write them so that the likelihood of making things worse is reduced to statistical insignificance. Personally I don't do anything without at least two separate and redundant backups.

I must admit most of my Time Machine backup drives were scavenged from discarded virus-infested or otherwise worthless Windows PCs, meaning they were free. Enclosures for them run less than $10 US. They're perfectly suitable for Time Machine. If and when they fail I throw them out. As long as TM backups are encrypted I have no concern someone might harvest the information they contain. Simplicity, redundancy, and disposability are attractive features for Time Machine backups.

If you must buy one though, a variety of external USB hard disk drives can be purchased for about $55. Considering the value of the information on your Mac they are probably well worth that expense.

I got the same pop-up after Catalina upgrade. I installed Malawarebytes (free version) which scanned and removed the malware. Did not pop-up after that.