How can i get rid of this line at the bottom of my screen?

This line only appears in certain apps such as my browser (Brave).
It's dark red because that the color of my wallpaper, if i select another app (like file manager) it'll turn gray.
I've tried setting a fully black wallpaper, the line still appears as light gray.

What is this, why is it here and how do i remove it?

The only weird like third party program i'm using is Windhawk, but i've killed it using the task manager and the line still appeared when i oppened the browser.

The best way i'd describe it is the window size not being fully stretched down and some pixels leaking from what's being.

This wasn't such a big issue until i got an OLED monitor, it could burn in, and i'd hate that.