Minetest is a block and voxel game similar to "Minecraft". In Minetest, everything is original, so you are not dealing with a copy, but with a free open-source game without ads.
In the single-player mode, you have two options: play in normal mode or use the creative one. In both, you can create your own maps or use the default Minetest's maps. These maps have a grid size of 62,000 × 62,000 × 62,000 blocks. Thus, you can build 31,000 blocks upwards or break 31,000 blocks downwards.
Minetest supports mods. Thanks to this, you can install many modifications, such as a fast map generator. As it was released a few years ago, the community has developed more than 1000 mods for this game.
In Minetest, you also have a multiplayer mode. You can create your own server or join others already made. Each one has a different configuration, and the tasks to be performed in each of them will depend on the host. In addition, you can play with other people on platforms such as Windows, Linux, macOS, and FreeBSD.
So, if you are looking for a completely free block game, you can download the APK of Minetest.