What problem does leaking the timestamp cause?

UUIDv8 gives you timestamp + counter + random.

The advantage is that lexical order and chronological order are the same and you still retain enough random bits that guessing the next generated timestamp is not easy.

uuidv8 does not contain a timestamp or counter unless you put them in there, it only contains a version and variant field. It's a very broad format that lets you contain whatever bits you want.

This library converts a uuidv7 into a cryptographically random but deterministic uuidv4 recoverable with a shared key. For all intents and purposes the external view is a uuidv4, the internal representation is a v7, which has better index block locality and orderability.