Big Sur will NOT recognize any of my external portable drives.

Ronnie, I have drives that I have to unmount/eject, physically disconnect, then reconnect for my Mac to work properly with them. I was told by a software developer that it has to do with Apple's new security in the OS. In my case, I can access the drives, open files on them but randomly I become unable to save changes to those files. I can save a new document on those drives but not update the one I opened.

Not sure if the same method would work for you but its worth a shot.

I don't know why Apple wants to protect me from myself but its very &%&#(% annoying.

If your Mac originally came with Sierra then you could erase your drive and reinstall that OS. Or if you had a TM backup with Sierra you could reinstall from that.

They must be formatted for use with a Mac.

How are you connecting them to the computer and are you connecting via a Hub?

Then do as @ QuickTimeKirk suggested and reformat

When you say Big Sur does not even recognize them - they are not mounting in Disk Utilities or not showing as mounted on Desktop ? Big difference so please check Disk Utilities.