To prevent a user activation from opening more than one fullscreen window, entering fullscreen will consume the user activation.
Right now fullscreen does not consume the user activation, so a single user activation allows opening as many fullscreen windows as possible. This is counterintuitive. Moreover, Chrome’s current behavior caused a security bug in the past where two different windows would go fullscreen simultaneously, with one of them spoofing browser UI without the user’s knowledge. Even though the exact repro in that bug is suppressed in M72+ by restricted activation visibility of UAv2, it still makes sense to fix the core problem.
Docs: none
Samples: https://output.jsbin.com/dudakil/
Explainers: none