Just wanted to resurrect this old thread to mention that I recently had the same problem with my 2021 Telly, which is out of warranty. I wasn't going to pay $5k for a full dealer replacement, and I also wasn't sure if any local shops would be up to the task. I was able to fix it myself after a few hours of headaches and swears. These two resources were the key to understanding how this all works, how it failed, how to fix it, and which parts were required:
This guy's youtube video is amazing:
And this technical service bulletin is also quite detailed:
https://static.nhtsa.gov/odi/tsbs/2023/MC-10239743-0001.pdf
And this part kit for the left-hand side mechanism assembly (different part for right-hand), which I had in one day from the dealer for about $40: 81610 S8000FFF
My repair was more difficult than most because there are some preassembled plastic parts which mount and slide along the inside of the aluminum rail and they don't seem to be replaceable (without the whole sunroof assembly) so I had to get creative and use more force than I would have liked. I also don't know how long my repair will last, so I'm just not going to use the sunroof. Having seen the plastic parts up close, these sunroofs seem pretty brittle and I wouldn't trust their durability at all. Definitely a weakness in this car. Good luck!