Has someone clear info on how Apex scaling works?

Hey.

Today after years of playing I bumped into (yet another) crazy (or am I) Apex way of doing things.

So here is my situation. On 3600x and 5700xt and 2k monitor I can't run Apex in stable 144+ FPS range (to avoid using vsync and freesync).

So I used AMD option of super resolution aka rescaling 1080p (1920x1080) to my 2k native. Picture looked worse (that's how old gen AMD super resolution works) but FPS were dead stable at locked 141.

Today I wanted to try to play with black bars aka scaling off, but Apex does not seem to allow that only offering borderless window mode.

What I noticed though when turning off scaling in AMD software, that Apex still scales my game to 2k if I use "Full screen" + lower than native resolution AND it actually looks better than AMD scaling AND FPS are more stable.

Never thought such option could exist...

Can someone explain how this thing (Apex) works? Does it have its own scaler that overrides AMD software settings?