i received help for my problem on the tech support in discord.
Solution for the update loop:
theres probably an old median verison running. get the new one (https://www.moddb.com/mods/medianxl/downloads
), and install it via gettin the files in your diablo 2 ordner and probably overwrite the old ones.
since then, the launcher now says "play" instead of update and its running fine now. [i uninstalled the launcher b4 updating median manually and installed it again afterwards)
thanks to @Gavin_K88 for the help.