GERD can be caused by LOW stomach acid.

You need high acidity to cause a proper stomach dump.

Here is the way it's supposed to work.

High acidity closes the entry valve (Lower Esophageal Sphincter) and

opens the exit valve (Pyloric Sphincter).

If you don't get enough acidity (because you've been eating Tums, etc.),

your stomach doesn't reach the acidity trigger point to dump.

Your sub-optimal-acidity contents just churns and backs up.

Research for yourself.

https://www.metacrawler.com/search?q=gerd+low+stomach+acid

You lose stomach acidity as you get older. You can replace it with betaine pills.

https://www.toyourhealth.com/mpacms/tyh/article.php?id=1454

NOTE: betaine suffers from propaganda like ivermectin does --- it's cheap and it works if you have the low acid version of GERD.