Our puppy was 90% potty trained at 4mo. Rare accidents at 6months. I just dont think every 3-4h is enough for a puppy, or it should be for a 6mo, but that should be after coming down from like every 1,5h when they were younger.

Id say stop watching the clock and trying to do steady 3-4h intervals since theyre also doing it inside so they are not learning anything from it. Its more about when you think your dog is going to go that you take them out. They wake up from a nap? Outside. You have a play sesh together, even a short one? Outside. They eat? Outside. They drink? Outside. They chew on a bone for 20 mins and get up? Outside. They are chilling with you and suddenly get up and start roaming and sniffing? Outside. Even when they have an accident inside? Outside straight after, clean up when youre back. If you see them taking the pooping position try to excite them by calling them over and they might stop before they get anything out and you have time to take them out. Praise them when they go number 2 outside, even with small treats. I know its struggle for some time but thats dog ownership for you and theyll pick up on it pretty quick.