TLDR: Settings > Accessibility > Zoom
After buying a new laptop, and suffering through some mild singeing of my retinas for the first week of ownership, and after relentless googling I may have found an answer that will work for you (at least it did for me).
My setup: Gnome, Wayland, Fedora 33, Dell XPS 15 9500
You should be able to find in the Zoom feature via Settings > Accessibility > “Seeing” > Zoom. Here you should be able to modify brightness, contrast, color according to your preferences. Set magnification to 1.0 (unless you want your focus to follow the mouse around). If you run into weird lingering visual artifacts from the mouse you can enable the crosshair and customize the color to be transparent (I also have thickness and length set to the minimum, and unchecked the “overlaps mouse cursor”, although I’m not sure whether these settings matter).
Lastly, for convenience and easy toggling, via Settings > Keyboard Shortcuts there should be an option for “Turn zoom on or off” which you can map to an appropriate key binding (mine is set to “Shift + Monitor brightness down”).
Credit goes to Bastien: Bug 741224 – new functionality request: Screen shader (control color temperature and brightness)
Best of luck!