Warning: 21w10a with Fabric 0.32.1 has a bug where right clicking any entity, not just villagers, will crash the game. This is not just an issue with EasierVillagerTrading; please don't report this as a bug! There is a bug report on the Fabric GH at https://github.com/FabricMC/fabric/issues/1360.
You need to use Fabric 0.32.2 (or later I guess) to get this to work.