@Anriandor, thanks for your fast respond. First of all, i did the thing "NONE-OPT OUT OF ALL BETA PROGRAMS" and other ones. (Just wanted to make sure if it is not 'none' so i tried them all.) Furthermore, I tried that you said starting as administrator and package thing but still same problem. My problem is about downgrading I suppose.
I can't see any announcement here, "https://forum.truckersmp.com/index.php?/forum/12-development-announcements/".
Should I wait for MP to update?
Last Update: I figured out how to fix it.
1. Go -> C:\ProgramData
2. Delete TruckersMP
3. Go to your TruckerMP Launcher folder, in my case it is in here C:\Program Files\TruckersMP Launcher, uninstall it.
4. https://truckersmp.com/download download from here again.
5. Let it update client (without wintermod) and you are done.