First the 100Ohm terminator is a bit low. They recommend 120Ohm.
Try and change the clock setting from:
cfg.clock = CLK_80MHz;
cfg.clock = CLK_24MHz;
I think 80MHz is too high or it is not a clean dividable to get 2Mbps.
I have a RGB LED LIN-bus example working with the Teensy 4.0 and Markus's LIN library.
Looks like jsimonkeller is making progress, lets see if he needs anymore help.