I was given a used 2020 MacBook Pro. How do I get rid of the previous owner's stuff. I currently have a older Mac and am backed up on iCloud.

WBGaul wrote:

I have downloaded some of my stuff, but the login and many files are full of stuff from the previous owner.

The previous owner must do this:

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

You won't be able to log out of the previous users Apple ID unless:

• You know the Password
• They have removed the Mac from their account

The device will be locked to this previous owner until they remove it. That way it prevents someone from taking your computer and setting it up as their own.