Increase resolution size.

[drakgoku]

Currently the resolution size is 1081x1081.

Can it be increased to 1024, 2048... ?

This resolution is not always good. For example, tangrams.github.io/heightmapper works with the monitor's resolution. Is there something similar for heightmap.skydark?

[delebash]

You can use Gimp a free image manipulation program to resample the image to what you want use lancos resample method. Google Gimp resample. You can also try my app where you choose the Unreal Landscape size and this resamples the image. https://terrain.justgeektechs.com/. Although I like some of the features of this app and am currently considering a rewrite.

[drakgoku]

If you use Gimp to resample the image with Lanczos, you may lose some quality due to this effect, especially if you resize the image by a large proportion. It also depends on the quality of the original image and the desired size.
Would it cost you a lot to implement other resolutions?

[delebash]

The highest resolution Mapbox provides is 512x512 for their images.