World Painter
WorldPainter is a wonderful interactive map generator. When I build custom worlds, they are often developed with WorldPainter.
Do visit the WorldPainter website a visit at https://www.worldpainter.net/. If you like the application, please do consider donating to its development!
Specific settings
I personally use MultiMC as launcher. However, that means that the Minecraft directory is not as expected, so WorldPainter cannot find a proper installation. Hence, I have a vanilla installation alongside which I hardly use, just to make sure that any tools that work together with Minecraft can find it.
To debug issues, set -Dorg.pepsoft.worldpainter.debugLogging=true (to enable DEBUG logging) or even =extra (to enable TRACE logging), as mentioned on the WorldPainter AdvancedSettings page.
I noticed that the output of WorldPainter displays the following:
{INFO } ( org.pepsoft.worldpainter.App) No supported Minecraft installation found; disabling biomes preview and Biomes Viewer
I don’t believe this is an issue though. A cursory look at the WorldPainter code tells me that WorldPainter requires a few specific Minecraft version jars (see BiomeSchemeManager.java with the DESCRIPTORS variable being seeded with a number of md5sums. A review of the commit history tells me the last update was for the 1.12 jar file, which probably means that the biome part here is not applicable for recent installations.