Block the user. It should be just one bot doing it in the lemmit.online instance.

To do so just, from your instance website, click on his name and search for the block function.

EDIT: For future reference you can automagically hide all (properly flagged) bots’ posts toggling the “Show Bots” in your profile, but you will lose the useful ones too and the one not flagged will still appear.

If silence is the real culprit you should try out a white noise generator, generally speaking it should overload/excite you less then music or human voices and could help you sleep faster.

Where I live silence during the night is not really an option, and I had had problems only when on vacation “away from civilization”, but small stuff like white noise, a fan or similar low but continuos sounds helped me out without asking for my attention (which happens with movies, music or similar).

There are even apps that simulate different kind of sound and let you mix them (like rain, birds, wind) but I didn’t have enough patience to really dig on this solution.