Why ALT+TAB=Windowed

So, basically I have a desktop and a notebook, both have weak GPUs for their screens (at least in beamNG)...
Desktop has a GTX 980 for a 3840x2160 screen
Notebook has a GT840m for a 1920x1080 screen

Since beamNG doesn't have an option to render the game in a lower resolution than the screen/window (like Frame Scalling Mode in GTA V) I need to play in fullscreen in a lower resolution, and that's where my problems starts:


1) Why pressing alt+tab makes the game windowed?
Every old game when you pressed alt tab it made the game minimized, not windowed, is there an way to make beamNG behave like old games?

2) When going fullscreen why it changes to the higher possible resolution?
Everytime I do alt tab, I need to go to the options and press fullscreen again, or just press alt enter, both ways the game changes the resolution to the higher possible, it's specially annoying on my desktop, since for some reason the higher possible resolution is 4096x2160, and the screen only shows 3840x2160, so everytime I need to find the options menu outside the screen on the left and then change back the resolution

While we are here...
3) Why windowed resolution is different from what i choose?
If I'm on windowed and I choose the 1920x1080 resolution, it doesn't stays at 1920x1080, it goes to something like 1880x1020?


I was away from BeamNG for a while because of situations like these (and the slow menus)... Yesterday I went to test the new patch and went through it all again, I didn't had much time to make tests but the windowed resolution problem I believe is that it sets the outside size to 1920x1080, but because of the borders the game is in a bit lower resolution, and It coooould be the reason why the game goes to the higher possible resolution when going fullscreen, it can't find a possible fullscreen resolution like "1880x1020" and throws to the higher possible

 

Actually I did some testings on this topic, and turns out that if the window has a valid resolution, and you press the fullscreen button, it'll go to fullscreen on that resolution, alt enter has a different behavior, it'll always go to the max res, doesn't matter what res is the window

(I tested it by resizing manually the window to valid and invalid resolutions, and then pressing the fullscreen button or alt enter... also tested using the borderless mode and worked fine with fullscreen button, but not with alt enter)

And about the "native" resolution, I use a 4k TV as monitor, 40KU6000, it's native resolution is 3840x2160, windows and nvidia control panel recommends this resolutions (and also puts on this resolution automatically when new driver is installed even on a clean installation), but for some reason it still lets me chose 4096x2160, but it never goes on that resolution automatically, just beamNG goes