As it turns out, the previous issue wasn't actually resolved. It is now, though!

Moonbow Bug Report, 2022-19-05: Unable to join friend via Steam

Attempting to join a friend's game via the Steam Friends List will result in the client throwing an exception, causing a pure orange screen to be rendered, with no in-game method to quit. Client will close the connection and fail to join the server.
After further testing, it seems the issue also occurs when attempting to join a friend's unmodded server.

The root cause of the issue has been located and patched, and will be releasing soon. I apologize for the inconvenience this issue may have caused.