iam think here will no way without “workarounds”. I was f… similarly way with opera sync, when something like id or some apiworker or smth “token” lost and all “sync” dissappear lol. but iam old fart and makes diff backups of my needed and important data (like logs, passes, bookmarks, seeds), doesn’t rely on some sync or ONE keeper (any, app, service, fd). always have an a backdoor way. thats my advice.
and of technically aspect try to restore your pc to earlier date, off internet before it (to dont catch some sync lol) and try to enter brave and extract bookmarks manually into file.
if this simple 1st hand trick will not work, u needs go deep into the system and find browser data into system folders (iam not on pc atm, doesn’t member exactly, but somewhere in local roaming for this user).
if you doesn’t have restore points, so… iam though there would be no solution. but lesson to make regularly backups. (not into one basket ofc).