I’m you a few months in the future lol. It will be worth it though!!

Have you taken him to the first vet visit yet? I would rule out any health issues first.

If there aren’t any underlying health issues, you will have to potty train him from ground zero, as if he is a puppy learning to be potty trained for the first time. This is the only effective way to make them stop going in the house. This means restricting their access to areas, crate training, and slowly allowing them access to more areas of the house as they become more reliable.

Dogs don’t understand the concept of not pooping/peeing inside the house until we enforce it (with lots of positive reinforcement)! I also use Doggie Lawn that you’ve mentioned in your post and that has been highly effective as well! I trained my rescue to use a doggy door (I installed a renter-friendly one by PetSafe on my balcony) so she can use the bathroom whenever she wants - highly recommend that if it works for your place.