There's limit how much you compress data, especially random ones (without pattern or specific iteration)
There is?
Yes. Compression is not a magic algorithm.
Compression works by removing redundancy of data.
Lets look at the following string for example:
abcbaaaaaaadbaaaaa
You would compress it roughly like this:
abcb[7*a]db[5*a]
With random data, you don't have such patterns. And therefore you can't compress much at all (at least not if it isn't an extremely shitty PRNG).
Same applies to encrypted data, because it will look like random data.
By the way, that's also one easy way to find encrypted data. Search a drive for data with high entropy.
If you find very high entropy -> most likely encrypted data.