Same issue here, Preform 2.20.0 uses at least 10% of CPU even when empty and doing nothing. Complex models (calculating printability / time etc) can peg a core i9 latest gen CPU to 100%, that’s all cores.
Logged a support ticket. Been a software engineer for decades, hate to rush to judgement but I smell a bug.
I notice there’s a 3.0.0 release this morning. Hopefully this bug has been fixed.