I'm experiencing the exact same issue described in this thread from over a year ago: https://forum.parallels.com/threads/major-issue-when-reclaiming-disk-space.346593/ I had to quit Parallels during a stalled "reclaim space" operation and now it won't restart at all. It is stuck on the "Starting..." pop-up. I'm on MacOS 10.15.6. Short of deleting my Windows image and starting over from scratch, has anyone found a solution to this issue in all this time?
Resolved, by deleting and re-installing the Parallels Desktop application (not affecting the virtual machine).