Based on the search results, the recommended level to advance to Act 2 in Baldurs Gate 3 is around level 7-9 if you have completed everything in Act 1. However, some players have advanced to Act 2 at level 5 or 6 and found it to be fine. It is also suggested to complete all the underdark and mountain pass areas before starting Act 2, as they can provide additional experience points.

If you are attempting a certain assault near the end of Act 2, it is recommended to be at least mid-level 7, although some players have found themselves a bit under-leveled at this point. It is suggested to seek out additional fights and side quests to level up before attempting this assault.