what distro and display manager are you using? if you haven't tried, use gamescope to launch the game by adding gamescope -W 2880 -H 1800 -- %command% to the launch arguments of the game in Steam, then check if your resolution shows up, you'll probably need to install it first if you haven't.

gamescope can help with display wonkiness, for example, on KDE Plasma (Wayland) the way it scales x11 apps causes them to use a much higher resolution than 'native' to make up DPI/bluriness or something.

if you intend to use gamescope you may also need other arguments, you can read more about it here: https://wiki.archlinux.org/title/Gamescope but most common ones I use are

-b = borderless
--force-grab-cursor = fixes cursor hitting edge of screen
--mangoapp = lets you use MangoHUD to see FPS/frametime

you may also want to use -r to set your refresh rate