Where is the PWM pin of the Dynamixel MX-106R?

That will take more work than you would expect. In general you will need a DXL shield to convert the full-duplex of the Teensy 4.1 to the half-duplex that the MX-106R needs. And I have not done this particular project myself.

“spidey” at this post mentioned some success with Teensy 4.1, maybe you can ask “spidey” directly for some more details.