Please write in your signature which RME recording interface and which operating system you are using. Thank you.
From another article I see you have Windows 10 with Ryzen CPU.
So I also have a Windows 10 Pro system and there are not the said problems.
A short video would be helpful to see what exactly happens on the screen.
My guess is that you have started TM FX and then started Cubase in full-screen mode, which would, of course, cover the other applications already open on the desktop. Then you would have to click on the TotalMix FX icon to bring it from the background to the foreground.
Which screen resolution does your monitor have?
I have Full HD 16:10 (1920x1200).
If you want to work efficiently in the DAW, then you need the full window size for the DAW.
The only chance is to get a larger monitor with higher screen resolution or to get a 2nd one only for the TM FX Window.
Another option is to have a small laptop or netbook running Windows and to use TotalMix Remote to remote control TotalMix FX.
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14