do things on their own
Could you describe what they do ?
no wifi around,
Do you mean you turned off wifi or did not find a wifi connection (that's different)
Bluetooth: probably not, it is short range. Devices could speak between them, but no access from outside most likely. Did you try to turn it off as well ?
You could read this:
https://www.macworld.com/article/676307/how-to-know-if-your-mac-has-been-hacked.html
If you were hacked, hackers would probably have taken care that nothing appears on screen. So unlikely.
May be you have tasks running in background ? Or is it automatic software updates (but that should not if wifi is off).
Topic:
Community
SubTopic:
Apple Developers