When the phone is unfolded, the screen size is not adjusted.
IDK about the folding devices, but wondering if something needs to be changes under the device settings? I found this regarding adjusting apps for full screen on other Samsung devices:
If nothing else, you might wish to contact Pixel Support:
Once on the link, scroll PAST the white search 🔎 box & choose a category to begin a help ticket. Support can also be reached by enail: firstname.lastname@example.org