I don't know if this is intentional, but I looked through the worldgen and there is no Bauxite or Aluminium in the oregen of the overworld.
You can only find it in the mining dimension or other dimensions, but not in the overworld.

Nevermind, Bauxite is in the oregen, I looked at the wrong file. But it's quite rare actually in the overworld.

Bauxite/Aluminum was specifically tuned and the spawn rate was buffed quite a bit, but it only spawn in higher elevations (similar to copper) so you won't find it if branch mining for diamonds, for example.