I was experimenting with adding a second display to the same graphics card, but I had removed it. I wonder if that was the cause of the problem. The link you shared, @greg, had me change the DISPLAY value in /opt/Autodesk/cfg/env.cfg from 1 to 0.
“Display” value env can be changed with flame’s setup utility. I wonder what does it means. I had some trouble with a new second monitor also and certain settings and I tested changing this value with any useful conclusion.
Thank you Andy and Greg. That solved it. I think I am not prepared for the “with great power comes great responsability”. This is my first venture into the “wonderful” world of Flame on Linux and so far have installed the OS and App like 30 times… Not ready to own a Ferrari.