Sorry to be a bearer of bad news, but definitely not! They’re both heavily categorized as aggressive type fish.
GBR are part of the chiclid family, which is a typically territorial type of fish. It’s often advised to keep a tank of that size a one chiclid species only because of aggression.
bettas are also very aggressive, and while can be kept in a sorority, it’s difficult and typically needs a heavily planted tank.
If you do manage to keep a peaceful betta sorority, a GBR will almost 100% cause problems. The bettas will go after it, probably mistaking it for one of their own (because it’s colorful) and the chiclids instinct is to fight and guard it’s territory. A 20 tall wouldn’t really even have enough mid-level swimming space for bettas and rams.
a peaceful school of tetra or rasbora will work well with a GBR. Do some reading on the types of fish you’d like to keep, theres a lot of good (and bad) advice out there.
I would not. I have a female Bolivian in with 2 female bettas in a heavily planted 40 gallon community tank. None of the fish have any problems whatsoever with any of their tank mates EXCEPT each other. My bettas have their territories and flare occasionally when the the other wanders in. But my Bolivian has zero patience for either of them. She has no problem with honey gouramis, cories, rummies and cardinals. But she hates those bettas. The problem is the bettas like to try to steal food from the bottom dwellers where Ramona is. She’s nipped at them good a couple times. I can’t imagine a smaller tank with more bettas working. But I find either the female betta or the Bolivian good community tank centrepiece fish