Browsers separate your data into profiles. Each profile has its own bookmarks, history, passwords, extensions and sign-in state, and switching between them looks almost identical apart from a small avatar.
Most missing-data panics are profile confusion: a work account opened a second profile, and the personal bookmarks are still safe in the first one.
Sync adds nuance. It is not a backup — it mirrors the current state, so a deletion syncs too. And sync can be paused silently when a password changes or a session expires.
Checking which profile is active, and whether sync says it is up to date, resolves most cases before anything is restored.