Yes, you can use it on the command line "ironseed.exe -force-device-index 1".
I'll do some research and see if I can find anything else that might help.
Hi again.
Someone reported the same problem but with a different twist here https://www.reddit.com/r/ironseed/comments/h901xe/no_video/
Sadly it hasnt worked for me, there is no second window appearing. But maybe it may help you in figuring out the problem.