upon further extensive tests involving gentoo-glibc, void-glibc and void-musl, I found out that void-glibc shows similar symptoms as on gentoo-glibc. On void-glibc I set the developement-test option in minetest and restarted xorg.

The very same symptom I'm having on Gentoo occured there. 

Minetest works fine on Void-musl.

On void-glibc I deleted the ~/.minetest folder as that also deletes chosen settings, but the issue persists and is even worse then on gentoo: minetest is marked as broken when starting and freezes the xorg server at startup aswell, while on gentoo: minetest starts up just fine, but trying to join a world sometimes results in minetest freezing.

Used Void glibc version: 2.32
Used Gentoo glibc version: 2.33-r7