macOS 11.0 Beta (Big Sur)
Joplin: 1.2.6 (prod, darwin)
If I open the About dialog to check my version, and leave it open for a few minutes, Joplin starts using 99.5% CPU.
Noticed because the fan spun up fast enough for me to wonder if the laptop was going to start hovering, and it stops as soon as I close the About dialog.
It does seem to take a bit of time to start, so I suspect it might only happen once the automatic sync starts? I can test further if this cannot be reproduced elsewhere. I have the automatic sync set to 5 minutes.
Thanks for your time!