Thank you very much for your answers! It was very helpful. Now I’m installing Fedora 36 on BTRFS on my laptop.
I found a step-by-step video tutorial how to install Fedora correct for Timeshift on encrypted BTRFS here: https://www.youtube.com/watch?v=bN8gGoBaZ5M
I will further create a @vm subvolume like discussed here: https://discussion.fedoraproject.org/t/qemu-virtmanager-in-combination-with-btrfs-and-timeshift/71011
Have a nice evening!