I'm having the same issue. MacOS 10.15.7, Evernote 10.5.7 build 2171 public. On initial launch, works fine. Seems like when the computer goes to sleep, and then I try to go back to Evernote later, all note windows are blank. I can see the list of notes (and the one to two line preview) but nothing in the note window. Also the pop-up telling you about the 10.5.7 update is blank. If I quit and restart Evernote, it's fine.
I've been having this problem for several releases now, not exactly sure when it started. Happy to supply additional info if it's helpful.