So I am in a sorta similar situation as you. I used to be on Zantac but I was quickly swapped to famotidine. I have been on it for a few years now and I agree that it is not as powerful and I still need tums.
I have been on intermittent fasting for around 6 months and I am down around 40 pounds. I did not notice a change at first but I have noticed it getting better as time is going on.
I even reduced the dosage and I am no longer waking up at night with a burning throat. I have even been able to go a day or two without famotidine but I will need a few tums throughout the day.
Eating or drinking acidic things will make it flare up for a few days but then it will get back to a manageable level. I have recently noticed that I am able to eat small amounts of the food that used to cause it to flare up without any issues.
All in all I am expecting that when I am down to my goal weight, I will no longer need the daily meds just so I’m not in constant pain and use it more when I am eating trigger food.
I don’t expect it to ever fully go away but I am happy with the results so far.
All that being said I am surprised by some of the things you mentioned. For one lemon and apple cider vinegar causes my acid reflux to flare up, I’m also pretty sure it breaks a fast. As for the protein, I have never noticed any correlation between it and my acid reflux and drink soylent high protein shakes daily.
I really can’t give any advice other than telling you my experience of getting results slowly. I really hope it gets under control for you, this is a pain I don’t wish on anyone.
Edit: forgot to mention I am on a 21:3 fast on weekdays and a 16:8 on weekends
Doing IF did the opposite for me. When I started I was having acid reflux regularly. Usually a couple times a week. I have been doing IF for 3.5 years now and I can’t remember the last time I had it. Perhaps it is the specific foods you are eating. I know there are some things I just don’t eat with an empty stomach because they will bug me.