Graphics enhancement mod no longer working after temporary use of motherboard display for monitor

I didn't have access to my 16:9 monitor for a while, so I had to use an old 5:4 one attached to the motherboard with graphics priority changed to there in the BIOS. Now that I've switched back to the GPU and am back on my widescreen monitor, this mod (https://www.cavestory.org/forums/threads/graphics-enhancement-pack.13920/) has suddenly stopped working altogether, with widescreen stretching and blurry texture filtering back. Fullscreen stretching happens with RPG Maker 2003 games like Yume Nikki too, which wasn't an issue before.

 

Maybe something like this?

How to Choose Which GPU a Game Uses on Windows 10

Windows 10 now lets you select which GPU a game or other application uses right from the Settings app.

www.howtogeek.com

Or maybe check the Nvidia Control Panel?

Set which GPU to use for individual programs or games for peak performance

We show you how to assign a default graphics card in Windows so you can make sure its doing its job.

www.techadvisor.co.uk

Might also set "Adjust desktop size and position" in Nvidia Control Panel to "Perform scaling on:" GPU, instead of Monitor.