In Xbox's defence, pretty seamless. I am signed into my xbox account, which is a Microsoft account. When launcing a game all that account auth bullshit is taken care of.

My wife has her own account, and our accounts are bound to our controllers. When you press the xbox button you are immediately signed into your profile, and it's instant. When she launches a game with her controller, she sees her saves and vice versa for me. With Baldur's Gate 3 it even keeps all her mods separate from my mod-free setup.

Some game publishers (activision, ubisoft et al) require their own accounts, and that's usually also taken care of automatically. The xbox goes and sets up a profile on that publisher's system on first game launch.

No idea why this is being downvoted, because it accurately describes the Xbox experience.