@Kungpao-Kitty Unfortunately, through the launcher you can only do Virtual Fullscreen, which is just borderless windowed that matches your current resolution for the most part; to get real fullscreen, you have to go into your user.pso2 file (with notepad or similar), and manually change the settings. Here's a thread that shows what to look for and what to change (though it is specifically about setting it to 4K): https://forum.pso2.com/topic/2831/i-fixed-my-4k-resolution-finally
I did end up finding the settings. They don't make it obvious. Very weird place and naming.