Why can't I destroy blocks or hit people in multiplayer and in single player on diamond dimensions?
It's just your game lagging, so if you wait a while you will see that the actions you have attempted to make will happen, but if you for example: break a block and it reappears, then you break a different block, only the first block will be broken. The only recommendation I have to fix this lag spike is to get rid of big mods, and get rid of mods you don't want. Doing either of these reduces the strain you're putting on your computer and reduces the lag.