I just found a great and handy tool for converting Minecraft worlds to Minetest, the how-to can be read at https://forum.minetest.net/viewtopic.php?f=12&t=13709&hilit=mcimport. Original post plus Linux command lines found here: https://forum.minetest.net/viewtopic.php?f=5&t=11146&hilit=convert+minecraft+to+minetest
I have heaps of old Minecraft world saves, though they're mostly not my original builds, I was wanting to convert them over for a while. I'm new to this, so every new helpful tool I discover makes me pretty happy.
I guess I could make the world saves into .mts files also, so that they could be shared.