Once when in Colómbia, I went to a home of one of my clients, who had a small garden pool filled with many male and female bettas, that were all getting along just fine. That was a big surprise, because I was used to having bettas in the US, all in separate or divided tanks. The one time I added a female and tried breeding, it didn’t work out so well, so I separated them.
While I’ve kept bettas in community tanks, they are food hogs, can be aggressive, and don’t interact as harmoniously as the other fish. Currently I have a mix of community fish in a 32 gallon tank, with cherry, blue, glass, and one bamboo shrimp, with no betta. I moved the one that had been there to a much smaller tank, because it was bothering some of the smaller fish, and had tried to eat one of the cherry shrimp. It sure looks more content, is very healthy, and it’s easy to control the amount of food it gets.
That may seem counter intuitive from a human perspective, thinking that a fish would like to have the biggest tank possible, but in my experience bettas do much better in small individual tanks.