Currently, the new multi-level list boards do NOT allow you to expand all subitems by default. For regular boards, you can click Control I and it will expand them and save as the default for the board view, but this isn't an option for multi-level boards. It is very tedious to go to each Group and select expand all subitems every time you go to the board. Does anyone know of a workaround?
Also, I put in a Feature Request so feel free to vote on it if you agree it should be addressed soon by Monday.com.