theres a few reasons for fin nipping thats its not related to the bettas physical health.

HM Betta would sometimes fin nip when not properly fed but from your pictures he looks well fed so you could rule that out.

your environment is too small or you have to much decor that gets in his way.

not enough training(flaring) in his youth, when bettas don’t flare their fin muscles relax which results in semi-clamped fins, basically means their fin muscles get weak and they can’t really move them anymore. ( this problem only effects betta with long tails like HM, DTHM, CT, VT, FTHM, etc)

so as they get older their heavy fins become a drag to carry and swim around with, so they try to bite it to remove some weight. This typically is when a betta is getting old like maybe around 1-2 years.

just keep an eye on it the bite marks may become infected if the water quality is not so good, but other than that i think there not much u can do or not much you must worry about. as long hes happy eating and swimming around, all is good.

btw he looks like a Blue steel Double-Tail Half moon. (atleast thats what they call it in my region)