My Berners have always been very easy to potty train, and my current girl took just 3 days to understand and 2 weeks to be trusted and reliable on her own. The breed is highly trainable this way - of course, it depends on our consistency

In my experience, the key to training effectively is to consistently show the behavior desired and reward for it (you're doing that) and don't allow the puppy to be wrong. Mistakes are reinforcing and each one doubles the amount of time to undue. The goal is 0 accidents inside and you can get it done in 3 days like I did. If accidents happen, they must be caught in the act or there is no learning.
I strongly advise against the use of puppy pads - that does nothing to show the puppy the desired behavior OR location and should only be used in desperate situations such as gone all day long and left alone in a kitchen - not ideal.
In my case, I picked up my girl a couple minutes after eating or drinking and took her outside to the same spot - when she squatted I said "go potty" and after 4 or so repetitions of this she learned the association of the action and word command. We stayed outside until she went by the way...patience
. Thereafter, I continued taking her outside every 40 minutes or so to empty herself with the same routine. They seem like they are never empty

While inside, I stayed within 2 feet of her at all times. This is tough for many and so I recommend tethering him to your waist. If she went into a squat, I was right there to pick her up and say "no", moving her outside. Any further than that, and we can't be on top of the action. I always left our back door open for my first Berner, and while he was generally good at going on when he needed he never learned to scratch the door or truly tell me he needed out should the door be closed...this can backfire....so with this girl, I never left the door open, so she learned how to manage with it closed and had to tell me and give me a sign.
We used potty pads while flying home on the airplane together in her bag and in the airport. Here's a great lesson of how this can backfire too: my girl was good and knowing where to go - outside is first choice. But for the first few days, she would go to the back door and if closed, she would turn and head upstairs straight to the master bathroom, where we had...of all things....whit
e bath mats. Funny, they looked like a potty pad. She peed the first time on the bath mat - very smart girl. So realizing this, I waited for the second instance, and when she turned to head upstairs I allowed her to go...following her...and waited until she got up to the bathmat and started to squat - then I quickly picked her up while saying "no" and ran her downstairs and outside. She understood that the bathmat was also not the right choice through clear association and it never happened again. This is the final key lesson - always catch them in the act in order to correct the behavior. I could have always prevented her from going upstairs to the bathmat but there was no learning in that - I needed to undue the thinking that the bathmat was choice #2. This is harder and harder to do the more times they have been successful going inside without being caught in the act and moved appropriately outside.
So just remember to focus on 1) very close supervision within 2 feet, 2) catch them in the act and move them promptly 3) set up structure to teach the behavior you want such as door closed and an indication they need out 4) reward profusely for going outside 5) set them up for success and take them out frequently so they cant be wrong
Good luck