Additionally, the dialog boxes (eg. the one between entering your login details and seeing the main window) should be set to a fixed size by setting their min-size and max-size the same. This would help with #597, as tiling window managers generally make fixed-size windows float instead of tiling them.
Unfortunately still an issue, even in Steamdeck OS 3. :(
Nothing extracted yet.
Steam's main window doesn't set min-size hints, instead opting to send a ConfigureRequest to the window manager if it goes below an acceptable size. The window manager, however, is free to ignore the ConfigureRequest and opt to send a synthetic ConfigureNotify for the old size. Steam does not adapt its display to the ConfigureNotify, and instead renders assuming the window manager will resize the window.
This can happen in tiling window managers, or window managers like gnome-shell that implement Windows 7-like side-by-side tiling.
While Steam should not assume the ConfigureRequest will be acknowledged by the WM and respond appropriately to the ConfigureNotify anyway, an easy solution is to set WM_NORMAL_HINTS with an appropriate min_width/min_height. This will signal to the WM that it should never resize the window below this size, ever.