You should follow up with Reddit. They can extend by a couple months if the request is complex, but they should have notified you of this in 30 days. If they don’t respond you’ll have to reach out to your DPA (data protection authority) and put in a complaint.
The GDPR is just regulation, you have to make the complaint if you want your DPA to enforce it. They don’t know you’ve made the request unless you tell them.
andrai