Terralith for 1.20.1 does the same as ITR: backports the new diamond generation from 1.20.2.
This makes the ore_generation data pack incompatible with Terralith. To fix this you have to disable the Ore Generation data pack in Materials and ores > Ore generation Overhaul and use the data pack below instead if you want to keep the ore generation data pack.
Terralith for 1.20.1 does the same as ITR: backports the new diamond generation from 1.20.2.
This makes the ore_generation data pack incompatible with Terralith. To fix this you have to disable the Ore Generation data pack in
Materials and ores > Ore generation Overhauland use the data pack below instead if you want to keep the ore generation data pack.ore_generation.zip