Could be fungal discoloration from being eaten by bugs. Might look for worm or bug damage in/around that dark spot to confirm. Wood can also turn that color when in contact with metal for a long time, but I'm pretty sure that's fungus. Should be fine to use as a walking stick as long as it's not soft and spongey at that spot.
Looks like old dried wood to me. It could be mold but not a rot
Could be fungal discoloration from being eaten by bugs. Might look for worm or bug damage in/around that dark spot to confirm. Wood can also turn that color when in contact with metal for a long time, but I'm pretty sure that's fungus. Should be fine to use as a walking stick as long as it's not soft and spongey at that spot.
Likely a form of spalting.
If unsure, let it take some hours of direct sun exposure to reach high temperatures for most molds