Ive been getting the same, sometimes alt f4 worked sometimes quit through task manager but just like you i had to also totally restart pc to solve it.

I've been reporting a bug in-game for months where if you log-out and take the daily rewards from the log-out screen, the game hangs. Can't activate the task mgr to kill the eso process as eso is stuck in the foreground and hogs focus. The only way to exit from fullscreen when this happens is to shutdown the machine (pc); I ended up switching to windowed so that when the bug occurs I can still interact with the task manager to kill the buggy eso process.

It happens with/without add-ons, with zero other applications active etc. Unfortunately, it doesn't happen every time you take the daily reward on log-out but usually does when it's something that goes to inventory, which is still often enough for zos to be able to reproduce it internally.

As far as I can tell the bug I'm describing has been around for probably a year or so and every now and then I get annoyed enough about it to initiate an F1 complaint.

No idea if this is the same or similar bug to OP.

But I'd be very happy to see it gone so I can play the game full-screen and non-windowed again and be confident of logging out and quitting the eso client without issue.