I have used secondhandn untreated bamboo spars on small sprit sails. I
filled any surface cracks with epoxy and gave the spars two coats of
polyurethan varnish. They were previously used as flag poles on
downhill ski slalom runs. They have served well.

Bamboo deposits silicon in its outer skin (bark?) which makes it hard,
abrasion resistant, and durable.Unfortuately the inner surface is soft,
soaks up moisture, weakens and breaks, or rots. After a capsize one set
of spars broke the next time I went out. You have to keep the inside
from getting wet. I don't know what the "treatment" is. Probably it
prevents this condition but I'd check before using it.

In Asia they weave thin strips of bamboo into sheets (plys) out of
which they make a very durable construction plywood. It is claimed to
last much longer than douglas fir plywood for concrete forming. The
sheets of plywood used in construction are too thick and heavy for
small boat hulls.