System Overload but more than enough CPU

Hello, I've got the Problem that Logic tells me my CPU is out of power while a max. of 20% is reached on my CPU.

Logic gives me this:

"System Overload - The audio engine was unable to process all required data in time.

You can try increasing the I/O buffer size, change the Multithreading option at Logic Pro > Preferences > Audio > Devices."

I'm working on a MacBookPro 15", 2019, 2,3 GHz 8-core i9, 32 GB RAM, OSX 10.15.7

What I've tried so far:

1. increasing buffer size to max
2. Setting the Multitherating to "Playbacktracks only" in Preferences > Audio

Both didn't help. I'd better avoid updating as other programs won't work with a newer OSX.

Any suggestions?

Kind regards, U:KUSTIK

Ulrich Schleicher