Very often they are cranky fish which do not care for friends. I have been lucky to have a long number which have been sociable with red tail Guppies and I presently have had a "Wine Glass" tank (48 inches tall and 7.5G )
This tank keeps appx. 5-6 male guppies and about 6 Pygmy Cories, a colony of "Ghost" shrimp and over the time I have had it several different Bettas - one only at a time. These have all been able to get along.
You will tell if the Betta is open to the idea. They can charge at the other fish, made or may not bump them swim around and follow the other fish (snail, shrimp) along and may or may not actually attack.
They all have their own personality
Actual biting /harming /stressing /attacking, etc. of the co-fish, you will need to remove the Betta of course.
Although general getting along when the Betta is junior age, before maturity, they often get along much better with tank mates as they commonly are grouped in one tank hatch / spawn when young.
Sexual maturity can cause them to get very possessive of their space /territory and a Betta which was fine with Mr. Guppy and friends might go on a murder spree.
Many people have had this experience. All is A-okay for days, weeks, months even over a year - you never know, and a keeper wakes up or comes home to bits and parts of fish, mayhem.
I have had an experience a long time ago. But, the Betta started to chase, stalk the snail and shrimp. I didn't notice exactly before but then recalled, a slight more aggression. Maybe keeping tabs on activity can help. And having a more spacious area for them.
Also have kept the Betta in larger tanks with a community. They need to be strong fish and a deep tank is not their friend.
I have had Betta which