No, because
and the OP asked very general, not about private messaging.
The OP did not clarify, as rinokeros asked, what they mean with “data”, so it’s a bit speculative, but it seemed a bit like asking if Twitter knows the contents of my tweets.
So the main point is, Librem Social is not meant for private conversations.
And that is exactly as advertised.
What is more concerning, IMO, is that (seemingly) encryption in Librem Chat is not on by default.
I’m very new to Matrix myself, so I assume this needs to evolve.
But, in contrast to Librem Social, this is not as advertised.
At least, the app makes you aware very prominently that you’re about to send something unencrypted.