Move mouse proportionaly between different resolution (and DPI) displays

Perhaps LittleBigMouse could help you out? It's an alpha application, but it seems to be focusing on the issue you're having.

DPI Aware mouse move across screens

Allows accurate mouse screen crossover location within multi dpi monitors environment. It is typically useful when using a 4k monitor and a full HD side by side.

Github: https://github.com/mgth/LittleBigMouse

Download (Releases): https://github.com/mgth/LittleBigMouse/releases

https://www.displayfusion.com/ has a feature that will mostly resolve this; it's very simplistic implementation. I have version 9.3 - not sure when it was added. NOTE: DisplayFusion is not free.

DisplayFusion > Settings > Mouse Management > Prevent mouse cursor from snagging on unaligned monitor edges

So, I had the same problem. TLDR; Due to lack of open source apps, (LittleBigMouse didn't work, DisplayFusion isn't free), I ended up writing a small application that does the job. Find it here: https://gitlab.com/rich4rd.macwan/mousemapper/tree/stable

I have two monitors, one 4k and one FullHD, both of almost same physical dimensions. The mouse movement between the two screens was a pain, because the 1080p vertical resolution of the 2nd screen(I have placed it on the right), is half the 2160p vertical resolution of the 4K screen on the left. Since I didn't find any free application for this, I decided to write it on my own.

It's a pretty simple tray application, that uses a mouse hook for getting the global mouse position and mapping it when it moves from one screen to another based on the resolution of the screens. Ideally, I should have put the mouse hook in a different dll (as suggested by microsoft), but I wanted something quick and dirty and it works. And it works only for two screens. Maybe if this application finds use, I will release a newer version with enhancements.

Hope it finds some use for people like me. It is not production level, but works fine for my case. Just putting it here if someone needs it :)