Since nvidia 535.x and new Steam GUI windows might not spawn and you have trouble using it. Here are ways to solve this:
$ steam -vgui launches Steam with partly old UI. Should work, but can't use friends network and if opening game properties webview will crash and reset.
$ steam --reset redownloads the steam runtime. Need to relogin. At least some Preferences are lost (compatibility / Proton for games, Settings like GPU acceleration). The new UI might launch though, at least until you restart your PC or restart steam. (https://wiki.archlinux.org/title/Steam/Troubleshooting#Steam_window_does_not_show_on_Nvidia_GPUs_after_the_June_14,_2023_update)
(Edit: This worked just once)
$ __GL_THREADED_OPTIMIZATIONS=0 steam
There should be almost no downside to this, prob some small performance loss. Source: https://forums.developer.nvidia.com/t/steam-for-linux-client-not-showing-ui-with-535-43-02-245/256178/9
In this thread this also was mentioned:
$ steam -no-cef-sandbox but this sounds unsafe. I suggest this only as the very last resort.
If you found a working solution, you can make an alias, e. g.:
alias steam='steam -vgui'
Alternatively, just install the flatpak. Since the flatpak package brings it's own runtime packages, it just works.