POD is what I am running. The game does work but it is in a little box in the middle of the screen. I have tried changing my monitor resolutions, always comes up with the same size small box in the middle.

Not complaining. I'm sure there is some reason why this is in this particular game. It just prohibits me from purchasing other games.

There are many games here on GOG that I would like to purchase but I'm not going to purchase them just to see if they work in full screen.

I don't know maybe some kind of info on the purchase page that says "yes this works in full screen mode in Win10, HDMI

I have a pretty standard machine for today. Win10, Nvidia. Plenty of ram. Using HDMI screen.

I think POD probably runs in a 640x480 resolution. Do any other (older GOG) games cause you similar problems?

Sounds to me it is something about your monitor settings (or is it a TV?). Check if it has any "zoom" settings. I get that kind of effect it I e.g. use my TV (with HDMI) as a monitor, and set in the TV settings that is shows the picture in its original format, not zooming it at all to fill the screen. So if the video resolution is any less than 1920x1080, then it will show in a smaller window in the middle of the screen.

Could also be some setting either in the graphics card drivers, or if the POD game uses e.g. nGlide and it has some settings related to that.

What is POD?

Maybe this? You need to turn on Scaling.

Eg. if you have a GF Card: check this image

I recommend "Aspect Ratio" option.

Yes! It was "Perform scaling on:" option. changed that to GPU.

Thank you very much.