I removed all "Extensions" in the Filemaker folder, now it is working
Filemaker Advanced 14.0.6 on a 64bit machine.
I also removed all extensions after trying everything else. Yes, that helped.
I had the same after one of the Layout in my solution crashed when trying to manually open it from the Layout menu, and Filemaker first behaved extremely slowly. Then Filemaker Advanced 18.104.22.1682_x64 would not open any file. I tried everything - for 2 hours - then removed the application and completely reinstalled the app.