I've been in a similar situation where I needed to quickly edit or combine screenshots, especially for tutorials or documentation.

If you're looking for something lightweight and online, you might want to try https://combineimages.online.
It lets you merge multiple images vertically, horizontally, or in a grid layout — all in the browser, no install needed. You can also tweak spacing and background color. Super handy when you just want to create a clean combined screenshot.

Not a full editing suite, but great for quick tasks.

3840x2400 not 2160 if it is 16:10 (which it thankfully does indeed appear to be)