In Fabric 1.18, Loom fails with the following error.

Mapping target name conflicts detected:
  METHODs software/bernie/geckolib3/renderers/geo/GeoProjectilesRenderer/[getTextureLocation, net/minecraft/class_897/method_3931](Lnet/minecraft/class_1297;)Lnet/minecraft/class_2960; -> getTextureLocation
There were unfixable conflicts.

If I change the getTextureLocation method in IGeoRenderer to something else (I used _getTextureLocation just for testing), then this error is not thrown.

Versions used:

Minecraft: 1.18
Loom: 0.10-SNAPSHOT (0.10.63)
Mappings: Mojmap
GeckoLib: 3.0.21 (Fabric)

Mojmappings are not supported and won't be supported due to the conflicts between Yarn and Mojmap. Until Fabric itself runs on Mojmap it won't be fixed.