Formatting a new hard drive

flawlessnyc wrote:

I figured out that pressing option command R at the startup brings you to the OS appropriate to your computer. Who knew?

From the link den.thed provided.

How to reinstall macOS - Apple Support

• Option-Command-R: When you press and hold these three keys at startup, Recovery might offer the latest macOS that is compatible with your Mac.

Normally I "Format and Reinstall" or "Format and Clone" then "Test" the drive before installing it in the Mac.

Now you need to:

1) Erase and Format, see > Use Disk Utility to erase an Intel-based Mac - Apple Support

2) Install macOS 10.15 Catalina on the new SSD, see > How to reinstall macOS - Apple Support

3) Then Migrate from the backup, see > Transfer to a new Mac with Migration Assistant - Apple Support

Ok thanks. What kind of SSD? Some just don't work with Macs, and as you're probably aware Apple doesn't consider them user-replaceable for a lot of reasons.

flawlessnyc wrote:

When I select the reinstall OS X I get the option to use Lion. My iMac only goes to Catalina. How can I adjust that?

You must first use the Disk Utility in Recovery to Format the new SSD.

If Recovery is trying to install Lion, then you need to format the newly installed drive "GUID Partition Map / Mac OS Extended (Journaled)" before you can Install macOS Lion.

Then after Installing Lion, you can Upgrade to Catalina.

Start from the beginning. What did you install, and why did you install it?

Writing an effective Apple Support Communities question - Apple Community

Here is what you can do in recovery mode:

Use macOS Recovery on an Intel-based Mac - Apple Support

For you, first use disk utility to erase/format the hard drive and then re-install the OS.

You need to install Lion - which probably came on your computer - and then upgrade to Catalina via Software Update/App Store.