Short story: For personal reasons I work on two Windows accounts on the same PC. In one of those sessions my tablet won't work fullscreen!
Now long story! I use two different Windows accounts for privacy issues, in my daily work account, which is the one I use the most to draw on Krita, I disabled Windows Ink from my Driver tablet options (Gaomon M10K 2018 model) since I had a lot of lag problems, that was last year, so it was an older version of Krita, but today I started Krita on my personal account and noticed that the tablet was more sensitive and nice to draw on, it turns out I never disabled windows ink on that account, but I started noticing immediately that I couldn't draw on parts of the screen that were too close to the edges, I blamed Windows Ink since it is the only different thing i have from my main session, so I went and disabled Windows Ink and pressure sensitivity was gone. So I returned to my regular windows account to check the settings and see what happened if I enabled Windows Ink, and it turns out that yes, i was working without pen pressure all this time :/ so I gave it a test to see if I had the same cursor edge problem as in my other Windows session... and it turns out no, it's working perfectly fine. So there you go, I can't draw fullscreen on one of my windows sessions when enabling Windows Ink but if I disable it, the problem solves... but I lose pen pressure. So summarizing:
Main Windows account: Windows ink enabled, pen pressure working, I can draw on the full screen.
Same PC, different Windows account: Windows ink enabled, pen pressure working but my tablet won't work on the full screen.
In both cases, pen pressure won't work when Windows Ink is disabled.

My PC setup: Ryzen 7 3700x, nvidia rtx 2060 super, Pen Tablet: Gaomon M10K 2018 model.
My soft setup: Windows 10 always updated, Krita 4.4.3.
My Krita settings (same for both sessions):
Renderer: Direct 3d 11 via angle, Scaling: High quality filtering.
Tablet Input API: Windows 8 + power input (Windows Ink)
Thanks for the help!
PS I forgot to mention I have two monitors, Krita is always maximized in my main monitor so I'm not sure if that has anything to do