How to delete data and reset macbook pro

What to do before you sell, give away, trade in, or recycle your Mac - Apple Support

And one other question. I had "File Vault" turned on on both of the above mentioned computers...

In that case just erase the Macs and surrender them to Apple.

Most of the steps in What to do before you sell, give away, trade in, or recycle your Mac - Apple Support are either inapplicable or optional. For example you do not need to create a backup and the steps regarding iTunes do not apply to Catalina or later. The only step you ought to follow is Step 6, which is to erase the Macs.

I saw nothing (might have missed it) in your link about turning File Vault OFF...

That's because if you encrypted those Macs with FileVault there is nothing else you need to do. Just erase them. Do not turn off FV; that would defeat its entire purpose. FileVault renders your data utterly useless to anyone without its encryption password — which also gets erased when you erase the Mac.

That process works for everyone who sells or recycles their Mac. so it is not too complicated for most.

If by "recycle" you mean dispose of in the garbage, you can always use a large hammer to destroy the computer so no one can access any data you did not remove. Wear safety glasses if using the hammer method.