I am a current mosh user too.

In mosh you can’t scroll backwards, due to how the implementation of mosh is made.

See https://github.com/mobile-shell/mosh/issues/774 and https://github.com/mobile-shell/mosh/issues/122

This has annoyed me for a long time so I am definitely going to give ET a shot.

As for the stuff about tmux I don’t know since I don’t use tmux.