Finally some progress.
I unscrewed the little screw that goes directly into the choke and untightened it a little bit which seemed to give a little bit more wiggle room. Afterwards, a few slow but firm pulls actually released the choke cable. I can now pull the choke open all the way, with a catch.

I still can't figure out how the spring fits into this picture so the choke will not stay open. I had to keep the choke open while pulling the clutch in. You need like 14 hands to do it but it can be done. As long as the choke was on the bike gave the signal of "i am about to start" and it did start on the second try. (Why my bike won't start without the choke open on a 80 degree day I don't know.. might be bad gas in the tank or something. It is kind of low)
It runs a little weird though. First I had to tune the idle speed again. Afterwards in neutral when I open the throttle it threw out some smoke after 5K rpm.. While I close the throttle, it sort of hesitates for a second or two at 2Krpm before coming back to regular idle 1K+change. I will change the oil tomorrow.
The geometry of the bike feels a little different. I hear a lot more cables squeaking when I turn the handlebar right/left and I feel like the handlebar is not straight. I did replace the old handlebar (which is when this whole choke thing started) with a stock one in perfect shape. The bike has been knocked down violently enough to bend the handlebar on the right side, while parked. I hope I don't have a misaligned fork or anything like that. I would know nothing about how to fix something that huge
Thanks a lot for your help.
Oktay