UPDATE (for the four people who read this already 
) - I managed to save the Library > Safari folder from another Mac that hadn’t suffered the bug (yet). So I’m not desperate to recover things anymore, but I would like to know how this happened. I won’t be trusting those bookmarks to Safari anymore, at least not without a non-Safari/iCloud-accessible backup!
I went to open a saved tab group this morning, and the group was empty. In fact all of the groups were empty. I don’t know how this happened, so I’m not sure how to get them back.
Unfortunately my backup routine has been pretty lax since I retired, so the best I could do was to try to restore the Users > me > Library > Safari > Bookmarks.plist file from a TimeMachine backup, but they only go back about a month and the oldest one didn’t resolve the problem. But I’m not even sure that this is the file I want.
Has anyone else had this problem? Any solutions? All of the regular bookmarks (Favorites and Bookmarks Menu) are still there, it’s just the Tab Group Favorites that was wiped of bookmarks.
This is on an M2 MacBook Pro running macOS Tahoe 26.2, everything is up to date.
