I didn't know that you have nvidia tho.
It should still work the same tho, nvidia has gpu scaling and full screen scaling mode, too. It's like that it has a different name.
Just try out using HRC as mentioned, if I launch csgo on win10 for example, my scaling mode just jumps back to "keep native", so I can't use stretched, that's where I need HRC for, because it changes the resolution afterwards.
But for normal "fullscreen windowed" all you should need is gpu scaling and scaling mode to fullscreen, works for AMD atleast, don't have csgo installed on my nvidia notebooks, so I can't tell you.