join the forge discord server via link, go to the #bot-commands text channel
typ in the command above and replace "<class-name>" with the class name you want to know
for example:
!mcp -c moj AbstractBlock
the bot returns:
MC 1.16.5: net/minecraft/world/level/block/state/BlockBehaviour
Name: ceg => net/minecraft/world/level/block/state/BlockBehaviour
Side: BOTH
AT: public net.minecraft.block.AbstractBlock
the new name of AbstractBlock is now net.minecraft.world.level.block.state.BlockBehaviour