There's the old sawdust & glue kind of patch. Late in life I am learning that there are stainable wood glues which puts a new wrinkle on this process. I'm still investigating, but maybe someone more familiar with the stainable glues can chime in.
Most inclusions are pretty porous, which can be good. Marine supply houses have shelves of epoxies that are designed to penetrate deep and fast to stabilize wood of tenuous strength. The stuff I have in the garage is "Total Boat," and it worked very well on some cedar damage around the porch. It's absolutely watery, and I had a hard time putting it on the wood fast enough.