Frustrated trying to cast video from PC to Roku Ultra

I've done quite a bit of searching on this already, but I just can't seem to make this work the way I'd expect. I've read the tutorials on connecting to a wireless display and on the options for projecting a display. I don't necessarily think it's a Windows 11-specific issue, as I've never tried this with a previous Windows OS and probably would be just as baffled.

Objective & Background: My goal is to play video files using WMP (or some other player, like VLC) and cast that video to my Roku device for viewing on a large TV. I have two monitors attached to my PC. Monitor #1, as labeled by Windows, is my "left side" monitor and Monitor #2, is on the right. Monitor #2 is larger and higher resolution, so it's what I consider my main or preferred display. I normally operate these monitors in extended mode.

I've set the Roku Ultra to accept screen mirroring, device connect, etc. I don't have problems finding & connecting to the Roku as a wireless display. But when I initiate casting, it always seems to cast the "wrong" monitor output to the TV. I get video on the TV, but instead of the media being played, the TV displays the desktop wallpaper of the monitor which is not playing the video I'm trying to watch. I do get the audio from the media file being played, but not the correct WMP video...only wallpaper.

I've tried changing the various Project Display settings, trying "PC screen only," "Duplicate," "Extend," and "Second screen only" but I haven't been able to get any of them to actually work in terms of getting the actual video being played in WMP to cast to the Roku/TV.

The closest was when I was able to set it somehow so that by sliding the WMP playback window off my active PC monitor, onto the "dead" PC monitor (in sleep mode because I had set only one monitor to be active) then I was able to see a portion of the WMP playback on the TV. But I obviously cant control the playback, screen settings, etc. from a monitor that isn't active. In a nutshell, I can't seem to get the video from the "active" PC monitor which is playing the movie, to show up on my TV. No matter how I set the Project mode, the TV seems to be receiving a cast of whichever monitor is not active. At first I thought if it the casted video wasn't showing the WMP video playback because it was on the "wrong" monitor, I could just move WMP playback to the other monitor, but then the video still doesn't show up on the TV. I just can't figure it out.

I wish there was a simple way to explicitly tell WMP to "cast active WMP window content to Roku no matter how screens are configured in Windows" or whatever. Maybe I have a fundamental misunderstanding of how screen mirroring/casting works.

I don't know if this will help or not, but you did mention you'd be willing to try other players (if you haven't already) and in VLC, you can start the video, pause and go to "Playback -> Renderer" and select the TV/Roku from there, that way you're casting the specific item you want instead of the 'wrong' desktop.

Let me know if it works.