After deleting (renaming) the file, the game went through a 'preparing' progress bar, which it didn´t before. After a short while the game window came up with an error message:
Game Crashed, may be caused by invalid Java Runtime configuration........ etc. Exit code 1
here is the current debug.log https://pastebin.com/nCULqfrb
and the Launcher.log https://pastebin.com/Xeyb3gSA
thanks for the replies and help sofar!