Borderless-Gaming VS Playnite

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

I've done something similar before with Playnite (an open-source PC game library manager), which has an HLTB plugin.

Playnite: The one with the most features and libraries available via addons and has a lot of options for customization. In my opinion the best one available for this purpose.

Here's a project for Playnite 11: https://github.com/JosefNemec/Playnite/milestone/9

As for my LGO, the only other app I've installed outside of the standard launcher was Playnite to consolidate all games into one place as Legion Space doesn't detect everything I have installed and I don't want to manage manually adding games to their launcher.

use playnite instead of the individual launchers.

Here is where I come in and recommend everyone check out Playnite: https://playnite.link/

When I care about supporting a developer or publisher and they offer their product on their own storefront DRM-free, I will often go there to buy. Or I buy from GoG which takes a smaller cut. Playnite lets me launch my Steam and non-Steam games in a seamless fashion. Steam still does a great job as a game installer/patch manager, and helps me discover new games. But I'm not locked into paying them a 30% fee, which is pretty brutal for some smaller publishers.

Game Launcher https://playnite.link/

For anyone with any of the myriad of HDR monitors that prefers to leave desktop mode in SDR RGB, I just discovered that the excellent Playnite game launcher has a feature where you can enable HDR on a per-game basis. Simply tick the "Enable HDR support" option under "Advanced" tab for the settings of the games that you want HDR turned on for. I was previously using the now-abandoned AutoActions for this, so glad to see there's an alternative in a tool I already use.

Not exactly what you are looking for, but I've been using Playnite to launch everything on my computer for years.