If we both have a file that is the exact same and we encrypt it with different keys, the blocks on the disk are going to be different and you won't be able to dedupe them.
Otherwise, encryption would not work very well if we were able to see the same data at the block level.
There are ways around that but we are doing software encryption before the data is written to disk so it's all going to look different.
Here is an article that talks about it: