Audio Performance maxed out way before CPU is maxed out


Mac mini 2018, i7, 32 GB Ram
Mac OS 10.15.7
Cubase 11 Pro

I have round about ⅓ less audio performance when I run 2 screens (1x4k & 1xHD).

But the much worser thing is that my CPU shows me that I still have minimum 70% inactive CPU Power but Cubase Audio Performance is red and the project dont play anymore.

Anybody have an idea what I could do here?

Thank you very much.

Best Ali