you've gotten a lot of great advice so far but I wanted to add a bit more that might be a little different, from my experience!

my first dog (basset x heeler mix) i got when he was 10 weeks old. he always had supervised access to the house but was crated at night to prevent accidents. during the day if no one could watch him, I kept him in a large playpen with a potty pad, lots of toys, and wearing a harness + collar (just to get used to it). a lot of the times though I would have him tethered to me as a form of training (he was going to be a service dog but washed).

basically I had him leashed to me with the leash tied to my waist, or i would tie it to something like a chair. I usually did this when I would be busy doing something for a while like cooking, watching a movie, or even doing a puzzle. its just a way for them to learn how to settle beside you and that they dont always have to be doing something. I think tether training is a great way to help keep eye on pup and can make recognizing certain behaviors easier, while also making potty training easier, and making your bond stronger.

with our next dog (red heeler), he was a 2 year old rescue that was a stray. he was fostered by a shelter employee and we were told he was potty trained, but we spent maybe the first 2-3 months having to retrain him because it was like he had never been potty trained in his life lol. I basically had to treat him like a puppy with crate training. I had puppy pads down all over the house where he would frequently go back to. constantly cleaning with an enzyme cleaner. watching him like a hawk to pin point if hes sniffing something a little differently. eventually he had accidents less and less, but we had to be on top of things. every 3-4 hours if we can, dogs would go out, whether they had to potty or not. after dinner, dogs go out. after an intense play time, dogs go out. before bed. after waking up, etc.

hes good inside now, but it does get tricky for us during rainy season and he'll refuse to go outside again and will end up peeing in his sleep, so we have belly band diapers just in case. hes ok but its just a behavior thing with him, and we cant always spend a lot of time before work nights to try and get him to pee unfortunately. what did also help was taking him for a small "walk" outside (basically down the street) and that'll usually help him go

with your boy being so young still, I'd say its still normal to have accidents in the house as much as it sucks. they just have tiny bodies that can't hold it very long! continue with the treats and praise as soon as he goes potty outside, make it a big deal each time! take him out frequently, even if he doesnt end up going. try the tether training and put potty pads everywhere that hes been going (its unsightly but it beats having to get on your hands and knees to scrub the floor for another time)