I found this beginner tutorial for Spark SL (the newly introduced Spark AR shader language) in a reply by @josh_beckwith on another thread. It looks like this wasn’t posted as its own message yet but (oh my) does it deserve to be!
I just went through all the examples and learned so much! All the shader files are commented and work like tiny lessons you can follow as you open and tinker with each project. It’s a wonderful resource. I don’t know if Adam is on this forum but if you happen to read this, thanks a lot!