I just skimmed through all the messages in the "Thesis" channel in the "TUM Master Informatics" and copied everything I found useful.
I didn't copy any advice about finding a topic and a supervisor, because it's not relevant for me (and there's a lot of stuff to copy).
And, everything written here doesn't pretend to be true, consult the official page first: https://www.cit.tum.de/en/cit/studies/students/thesis-completing-your-studies/informatics/
I have organized the info into 5 topics:
Preparation and thesis registration
Thesis submission and Deadlines
Last update time: 3rd December 2023