Your system information

• Steam client version (build number or date): steam-runtime_0.20201203.1
• Distribution (e.g. Ubuntu): Arch
• Opted into Steam client beta?: [Yes/No] No
• Have you checked for system updates?: [Yes/No] Yes

Please describe your issue in as much detail as possible:

The steam client and startup dialog don't provide any window manger hints, which means dialogs get treated like a normal window. This is mostly annoying when using a tiling window manger, which will just tile the dialog as normal window. This is just more of a nicety.
For example the info provided by steam can be viewed with xwininfo:

xwininfo: Window id: 0x2000008 "Steam"

  Root window id: 0x1e7 (the root window) (has no name)
  Parent window id: 0x1e7 (the root window) (has no name)
     0 children.

  Absolute upper-left X:  2648
  Absolute upper-left Y:  40
  Relative upper-left X:  2648
  Relative upper-left Y:  40
  Width: 940
  Height: 1028
  Depth: 24
  Visual: 0x27
  Visual Class: TrueColor
  Border width: 2
  Class: InputOutput
  Colormap: 0x2000007 (not installed)
  Bit Gravity State: NorthWestGravity
  Window Gravity State: NorthWestGravity
  Backing Store State: NotUseful
  Save Under State: no
  Map State: IsViewable
  Override Redirect State: no
  Corners:  +2648+40  -8+40  -8-8  +2648-8
  -geometry 940x1028-8-8

  Bit gravity: NorthWestGravity
  Window gravity: NorthWestGravity
  Backing-store hint: NotUseful
  Backing-planes to be preserved: 0xffffffff
  Backing pixel: 0
  Save-unders: No

  Someone wants these events:
      KeyPress
      KeyRelease
      ButtonPress
      ButtonRelease
      EnterWindow
      LeaveWindow
      PointerMotion
      ButtonMotion
      Exposure
      StructureNotify
      SubstructureNotify
      FocusChange
      PropertyChange
  Do not propagate these events:
  Override redirection?: No

  Window manager hints:
      Client accepts input or input focus: Yes
      Displayed on desktop 2
      Process id: (unknown)

  Normal window size hints:
      User supplied location: 2650, 42
      User supplied size: 940 by 1028
      Program supplied minimum size: 940 by 1028
      Program supplied maximum size: 940 by 1028
  No zoom window size hints defined

  No window shape defined
  No border shape defined

Where in the window manager hints would provide a window type in other applications.