Borderless-Gaming VS Magpie

You can. I use it to persist settings in my app Borderless Gaming https://github.com/Codeusa/Borderless-Gaming

This and this work, but they mess up OBS recordings so I stopped using them

Yes you can do that with any ultrawide. Simplest way is to just play windowed mode with a 16:9 resolution. If you want it to be 16:9 borderless windowed in the center of the screen you can use BorderlessGaming with a "Set window size" config, though that approach can be a bit inconsistent sometimes.

I don't know if its a fix, but Try grabbing Borderless Gaming. See if you can force it into a resolution you want. I would try it myself but...

Turn off screen rotation lock and rotate the display so it's portrait. This allows us to launch the game without issue into windowed mode (it's full screen landscape that's the problem). Now rotate the screen back to landscape, game will still be running in a window. Now use Borderless Gaming (or your favorite borderless window full screen app) to make the window into full screen. https://github.com/Codeusa/Borderless-Gaming/releases/tag/9.5.6

You could try Borderless Gaming - Free version BorderlessGaming9.5.6_admin_setup.exe - July 2019: (https://github.com/Codeusa/Borderless-Gaming/releases/tag/9.5.6)

Borderless Gaming is another free alternative that doesn't do anything fancy like improving the image quality but can also do the job of making your games fullscreen: https://github.com/Codeusa/Borderless-Gaming/releases

depending on the game, fsr(or dlss if you have the option) may be available in options to help you out, otherwise you could give a free option a go, such as Magpie

For games that won't go full screen, at least we have Magpie as a last resort. The experience won't be as seamless though...

Another thing you can try is playing the game in a borderless window at a lower resolution and using Magpie to upscale it to fullscreen. Magpie offers a variety of upscaling options that can produce a less blurry image than the bilinear interpolation that is typically done when upscaling by the GPU or display.

Configure VLC to play the video in an extra window with the same resolution as the video source and upscale the window to fit the screen. On Windows 10 the FSR upscaling can be achieved with Magpie. On the Steam Deck the system built-in FSR/CAS combination is used.

Something else that may also be of interest is Magpie. It's a tool to upscale windowed content into fullscreen with a variety of upscaling methods available.

also using enabled antialiasing in game settings (or even globally set in video driver) consume much less resources then rendering full size bigger resolution image for reducing aliasing. there are also such tools like Magpie (https://github.com/Blinue/Magpie/blob/main/README_EN.md) or Lossless Scaling tool from Steam. they enable FSR supersampling to any game on any GPU.

https://github.com/blinue/magpie https://store.steampowed.com/app/993090/lossless_scaling/

To everything that the community has said, I also want to add that No Man's Sky has FSR tech (the game runs at a lower resolution and it's upscaled). You can use Magpie or even better, Losless Scaling to create a similar effect in SC and win some extra frames :)