Why don't some Xbox games allow full screen gaming?

What Wolfenstein game are you referring to? There are currently four Wolfenstein games on PC game pass, five if you include the much older RTCW.

With the exception of RTCW, all of these have full screen, full screen borderless and full screen windowed.

What happens if you hold down the ALT key and tap Enter? Does it full screen now?

probably overscan The game saves some processing power by not rendering those parts of the screen.

Not sure you can do anything about that on the laptop.

To be honest Xbox consoles typically don't allow you to control or manipulate the cursor while playing games in full-screen mode. The cursor is usually managed by the console's system software and is not accessible or adjustable during gameplay.

do you run the game in full screen or in windowed mode

if your run the game in windowed mode the resolution will be locked to the monitor set resolution.

some game as a feature that allow you to upscale or downscale the game resolution this feature (usually called scaling) would allow you to scale the game rendering resolution

if its not present the solution would be to

a. change the monitor resolution prior of launching the game

or

b. set the game in full screen mode (in the game video setting) then you should be able to set its resolution

Trial codes do not change your account status to gold. It only allows some aspects of online multiplayer. There are some game modes/games that don't work with trials and require a full gold subscription.