Borderless-Gaming VS dxwrapper

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

Then, download this and place the files inside the game directory (C:\Program Files\Maxis\SimCity Classic).

There's also dxwrapper that implements old DirectDraw/3D interfaces with newer D3D9 api for better compatibility with newer Windows versions:

https://github.com/elishacloud/dxwrapper

FYI: The Space Bar re-release features Elisha Riedlinger's DxWrapper (https://github.com/elishacloud/dxwrapper), whose config file is otherwise stock with just FullScreen enabled. I strongly believe they didn't properly test it.

RTX Remix uses a custom d3d9.dll though so you additionally need another wrapper such as https://github.com/elishacloud/dxwrapper to customize which dll should be loaded since by default d3d8to9 uses the default system file which will result in translated calls not being redirected to the path tracer used by Remix.

If you have a GPU that supports DXVK (Basically it forces DXVK to run the game in Vulkan intsead of it's usual DirectX 9, which the DX9 version hates GTA IV and while GTA IV hates DX9 back) and has more than 2GB of VRAM (DirectX Vulkan), then I HIGHLY recommend it: https://github.com/doitsujin/dxvk/releases (Use this guide to install it: http://ant-sh.blogspot.com/2020/07/gta-4-stutter-choppiness-fix.html. If you want aliasing AND DXVK, use this guide: http://ant-sh.blogspot.com/2021/01/antialiasing-with-dxvk-and-gta-iv.html. If your GPU doesn't support Vulkan, use DxWrapper: https://github.com/elishacloud/dxwrapper/releases).