In a 10 that’s a solo fish. They are predators and 10 gallons does not give prey a chance to escape. Think of it like keeping a red wolf on a 29. Not ideal, but enough for the fish, but any tankmates are toast.
I just saw Crenicichla compressisceps (dwarf Pike cichlid) on Wet Spot Tropicals list, although I'd be hesitant to keep it in a 10 gal, maybe with no other fish(?) or maybe a 30-50 if other fish are to be housed with it).
The ones on their list are wild caught Brazil, , so I'd also be wary if your tap water is not naturally soft.
BTW below is Betta albimarginata (previously mentioned), which might be a more apropos for a 10 gal.
It is a mouth brooding Betta from Borneo.
Another wild type below
Betta edithae from the Malay penninsula
It is another mouthbrooder, spawning above.
Other options for nano tanks like 10 gals, are some of the killifish available these days.
Fundulopanchax sjoestedtii above, below Pachypanchax playfairii from the Seychelles islands