I've also experienced this issue for over a year or more. I'm running on macOS Catalina 10.15.7 (and can't upgrade any further due to iMac being out of support).
However, what I have noticed is that the 100%+ cpu usage does seem to occur more frequently if you have been editing a note and leave your text cursor in the note - i.e. it remains open.
The other aspect I'm aware of is that I'm logged into Evernote on several devices (iPhone, MacBook) - so wondering whether it's some kind of sync issue?
Other than that, it's tricky to reproduce, just seems to kick in randomly and consume every scrap of cpu cycle it can on the desktop versions. Easy to spot when it happens are the fans kick in after 30 seconds.
Would appreciate a statement from support on when we can expect a fix, or it's going to be a new solution for me.