betta community
It IS possible, but maybe only among "littermates".
My grandfather had several male bettas in a heavily planted tanks. They were long and shallow and who knows how many gallons. Coffee table sized. He also had a good dozen females in a tank with some similar shaped tropicals. That was a fancier tank with more decorations and clear areas as well as plants. Fights and posturing would break out now and again. Rarely was there any severe injuries. Once in a while a newly introduced fish was either too belligerent or became a target. They got to live alone or go to a pond in the back yard.
Singles seemed unpredictable when introduced to natural settings. They flared quicker and brought up hostility levels. Some seemed to hate certain colors.
Even at present, our two blue females would prolly fight to the death. The one even displays at the blue male across from her all day til he showed a stress bar and we turned the tanks back to back. She ignored the red male on the other side.
I am going to try to duplicate some of his freshwater setups this summer, now that the fish bug has bit me hard.