Macbook throttles to 0.8 ghz

Have you tried an SMC Reset? The SMC Reset procedure for a 2019 model is different than earlier models so read the SMC Reset instructions very carefully:

http://support.apple.com/kb/HT201295

Also a power issue can prevent the CPU frequency from going about the 800MHz idle speed. These USB-C Apple laptops can be extremely difficult to troubleshoot as they don't behave like a normal laptop (or any previous model Mac). Is your charger connected directly to the laptop? A multi-port adapter, dock, or hub may not allow the full power of the charger from reaching the laptop. Also disconnect all other external devices to be sure none of them are causing a problem. Also try connecting the charger to the right side ports to see if it makes any difference.

Reboot the laptop. I find it is best to restart a Mac once a week (or at least once every other week).

Try running the Apple Diagnostics to see if any hardware issues are detected.

Sidecar is there, but I can't recognize anything else, since you chose to post a low resolution copy of the process viewer window on the forum.

Sidecare uses a lot of resources. Etrecheck's printout can tell us what else is taking up your system resources:

https://discussions.apple.com/docs/DOC-250002463

Please run Etrecheck. We can know more by what's running in the background to see if the speed throttle is cause for concern. Many optimization software erroneously measure what's going on the machine, and only give a placebo effect for fixing things. Best to know what genuinely is going on in the background, and then we can help you eliminate any problems.

RunCat may need to be updated for your new OS.

Elgato requires a lot of resources. Make sure no other programs are running other than it and Toast.

NordVPN should only be used if you need to access a VPN only service. VPNs slow down traffic a lot on the internet.

CleanMyMac is a virus, to remove it, use AppDelete from Reggie Answorth to remove while booted in safe mode (with shift key)

Good things:

your internal SSD is runnig up to speed

your computer was not staved fro RAM at the ti eof tesitng

This could have a bearing on your performance issue if this extrenal drive:

disk3 - Generic STORAGE DEVICE 7.86 GB

External USB 480 Mbit/s USB

disk3s1 (MS-DOS FAT32) 7.86 GB (2.33 GB used)

has data stored the your apps need to regularly access. It is running at USB2 speeds. This is not a problem for backups made during idle periods but it should not be used as, say, a location for active scratch disks.

This was not an issue at the time of testing, but it was last week:

2021-06-08 13:11:09 photoanalysisd High CPU Use

This article talks about the common photoanalysisd resource hogging issue and a simple way to deal with it:

https://apple.stackexchange.com/questions/310594/what-is-photoanalysisd-and-why-is-it-using-77-of-my-cpu