To find diamond temples you need to be far enough away from everyone else to have a chance of finding a temple that hasn't been raided
Diamond temples are in a spawn that looks like: A lot of grass maybe a farming biome. There are 80 diamond blocks
The diamond blocks are underneath the middle part of the temple and there are many monsters around the diamond blocks
They take a long time to find and i like traveling in a straight line mostly North West
I play on the amazon underground server so there is a lot more chance of finding a temple unraided and close by