alexanderzhirov Thank you for the link, now i understand your issue.
Looks like someone have reported a similar issue https://github.com/mltframework/shotcut/issues/1057
"I had to do Edit->Paste and after that, I could drag and drop again. Shotcut seems to store the timeline information somewhere outside, so that even a clean reinstall didn't help."
Think i would try moving the folder: /home/user/.local/share/Meltytech/Shotcut to a temp folder, and see what happens if you start Shotcut, it should just recreate a fresh version of the folder, and all the settings should be reset...