So #7238 happened.
After that and hours of cleaning up the tabs trying to figure out where are the ones I really had before and which ones were added during the "sync", I've decided to take a snapshot to be able to restore the stuff once enabling the sync again.
It turned out, the tabs after restoring the snapshot got restored only for the current window (the same one I took a snapshot at). As far as I can understand from UX perspective snapshots are indeed workspace-related, not window-related. So, this sounds like a bug, since the rest of the windows are untouched (300+ tabs open in others).
expected it to restore all the tabs across all the windows
0.99.126.4.1-beta
Monterey (12)