Magicavoxel is really user friendly and doesn't take long to get the hang of.
Magicavoxel download:
https://ephtracy.github.io/index.html?page=mv_main
This is a simple 30min tutorial on how to use it:
https://youtu.be/uKOBIHSgIwI
These 3d models can be minted as NFT'S