Is your feature request related to a problem? Please describe.
Occasionally I get the problem where I'll update my graphics drivers or something and Minecraft will start running at 60hz again instead of my native 165hz. When that happens, tabbing in and out of Minecraft is extremally slow and there is a black screen for 5-10 seconds because it has to switch refresh rates. In order to fix this problem with Sodium installed, I have to remove Sodium and all the mods that depend on it from my mods folder, open Minecraft just to switch it from "1920x1080@60hz" to "1920x1080@165hz," and then add the mods back and relaunch Minecraft. Its kind of a pain, and I would assume to be a simple fix.
Describe the solution you'd like
My solution would be to just add the resolution slider to the settings, it would be nice to have.

What's the status of implementing this slider? 0.5.0 was released a long time ago, maybe bump up issue priority?

This issue and the other issue you commented on can be closed for being part of #46 which includes both of these aspects. #46 is implemented by the open PR #2296.
Edit: #46 has been closed with reasoning given in a comment there.

There is a PR for it, #957. Although it might be a bit out of date.

I'll mark this as planned for 0.5.0, but in the meantime, you can do Shift + P to bring up the vanilla menu.

Oh I didn’t realize you could bring up the vanilla menu