I've recently started DMing, and my biggest surprise when I looked into this is just how poor the general tooling was when I looked for it.

I found the user experience of Roll 20 horrible. I fumbled my way around the interface, eventually sort-of getting some maps going but the scene "transitions" were me just deleting the previous tiles because I couldn't work out how to set out proper scenes.

A lot of the other tools were random "download this .jar" applications which didn't run well at all.

I was fully prepared to throw £20 at a good solution for designing a few maps I could then easily put into roll20 to coordinate a session or print out for offline sessions.

But while there were a few good open sets of raw tilesets, the actual tools for putting together tilesets into dungeons seemed completely missing.

For such an established market I expected to be inundated with mature tooling, but even the official stuff like "d&d beyond" is only just coming together and still mostly lacks the tools for actually running a session.