Gut feel based on common tech platform procedures, right? (As opposed to a sourceable certainty.)

It would be PR suicide to disclose exactly what data is shared. Cambridge Analytica is a prime example of a PR nightmare with similar data.

I don't even need to look at reddit's terms and conditions to know that there is practically nothing stopping them from handing this kind of data over legally for anybody who hasn't submitted GDPR deletion requests. I never trust compliance of laws that cannot be verified independently either because i've seen all kinds of shady shit in my career.