ISSUE
The Steam client doesn't function like a normal macOS window. It doesn't work with Stage Manager, and it can launch itself inside of other fullscreen app's spaces (and then it's super difficult to remove it without restarting).

OS
macOS Ventura 13.2

These are both the same bug. Do not think I'm reporting two in the same post, I'm just showing off different ways it manifests itself.

STEPS
- Fullscreen an app, so it appears in its own Space in Mission Control.
- Launch Steam
- A desktop space will automatically be focused.
- Navigate back to your fullscreen app space. (I have things to do while the Steam client opens)
- Observe: The Steam client will launch within the fullscreen app space! Without external window management features, it's extremely difficult to get it onto the normal desktop without restarting Steam entirely.
- Video[cln.sh]

EXPECTED
Despite a fullscreen app space being focused, The main Steam window shouldn't be able to launch in it. It should behave like other app windows and appear in the desktop.

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STEPS 2
- Open some apps with Stage Manager enabled. Put them in different stacks and whatnot.
- Launch Steam
- Try switching stacks and moving Steam to other stacks
- Observe: It's like Stage Manager doesn't even know Steam exists!
- Video[cln.sh]

EXPECTED 2
Steam should just behave like a normal window and work with stage manager. Instead, it just sort of stays where it is.