I've got a 2017 cabrinha spade with a few small chips on the board. Nothing major but a few of the have exposed the bamboo underneath.

What's the best material to repair these chips with? Epoxy glue, surf epoxy/fibreglass resin, something else?

These boards are very poor quality to start with.

If the Bamboo has become exposed, you'll have to patch it with fiberglass cloth and epoxy or else it will suck water in, transfer onto the blank and will eventually delaminate.