Hi all!
I'm not claiming this answer as my own, but found this at https://community.ultimaker.com/topic/33478-cant-select-any-objects/ :
"I have MacOS 11.0 - Cura 4.8 - and fixed it with - Adding Cura to "Security & Privacy" - "Privacy" - "Full Disk Access""
I'm on 11.1, / 4.8. On applying the preference change, it worked for me.
Enjoy!
Mikey