Error when running (only) GarageBand: "Heavy memory usage" AND Disk stops sometimes (overload)

I really don't know what else I can do. The only app I'm running is GarageBand. I've moved all the 2GB of sound files to an external disk. I'm only using 1/3rd of my on-board hard drive and only half of the RAM. So why am I still getting error messages and overload disk stops when running ONLY GarageBand.

Maybe there's something wrong with my hard drive (see two screenshots of "Mac hard drive" and "Mac hard drive data"--why are there TWO?).

Anyway, I appreciate any wisdom that can help me.

Hard for me to believe my 2019 MacBook Pro running Catalina is choking on GarageBand.

(And btw no, I won't be upgrading to Big Sur quite yet. I wanna handle one problem at a time.)

Thanks in advance.