Thanks much for the help!
Yes, I'm still using the SP3 native monitor as well as the secondary 4k monitor. ⊞+P shows "Extend".
If I have the focus on a window and I move it to the native monitor (e.g., when configuring logging, move the channel selection window over to the native monitor), then the modal dialog comes up in the foreground on top of the window.
If I do the same thing and leave the window on the secondary monitor, then I can't find the modal dialog and I have to kill Tune via Task Manager and start over.
I'll try to recreate again to to try David's experiment. (clicking on the M1 Tune icon on the bottom)