My mouse lags if I don't have it in windowed mode so I chose the fullscreen windowed mode in the f1_resdll file but it looks like it's 1024x768 instead of 640x480. I would like the original resolution because the words are pretty small but I can't change the resolution with the windowed fullscreen enabled. I can change it but it doesn't seem to stick. Idk what's going on. Windows 10.

In the video options, deselect the Scaling x2 option. Once done under Fullscreen all resolutions will appear up to the lowest 640x480.
However, I advise you to keep the resolution 1024x768, and in the Panel Scaling, for all the voices, except "Movies", select "FILL", so as to adapt the image to your monitor.
Do not do this for "Movies" or the videos will be seen incorrectly.

I Forg, however, some areas of Fallout 2 will be seen with black borders, because the default map is small. For the rest you will see, you will see perfectly!

I thought so as well, but it turned out that often they are just hidden. Disable EDGE_CLIPPING in f2_res.ini to see the full area (for example, starting area specifically).

I tried, but it does not work for me. There are always black borders.

Strange, I get the full screen.
Full ini here https://pastebin.com/U3LGfCYm

Nothing, I do not know why, but it does not work for me. It 'does not matter. Thanks anyway, even if it's a real shame ...

I succeeded through f2_res_Config.exe, in manual.
However from how you see from the image, the visualization of the game is seen in a different way, compared to yours, how come ???

Have you used another mod ???

Didn't notice it's about vanilla... I have RP 2.3.3.

Here is the mystery revealed! Interesting! but does this mod add or modify texts / dialogues in the game?

of course, lots