so I just tested and i also can not play them offline... which is weird, it should work... I even found a youtube video from 1 month ago showing how to set it up (set as home console and set the console to offline, which is how it should work) but for me it does not work.
apparently some games do not work offline, but I tried games that should 100% work and they didn't. so this is really weird not gonna lie
edit: SOOOO I found out what is going on, and this seems like something that has changed within the last 12 to 18 months or so (that's where I find most of the issue reports)
it seems like, you have to play the games you want to play offline before going offline. so if you wanna play Forza Horizon 5 offline with gamepass you will have to have played it within the last 30 days before turning your console to offline mode for it to work.
I just started Dogeball Academia, then set my system to offline, and it worked offline. I then tried another gamepass game that should work offline but that one didn't work, because I haven't played it within the last 30 days.
this is a very bizarre change and tbh seems almost like a bug and not like it is intended, if it is intended it sure sucks