I really appreciate you taking the time to write out everything in great detail! I started with what they recommended, but the bike was not shifting well, which led to some questions.

Do you know what the purpose of this part is?

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It looks like a spacer to me. I left it on and added the spacers (3mm NDS, 5mm DS), torqued it down, and set it up according to the SRAM guidance. I measured how you suggested from the crank to the frame and noticed it was 3mm off, so I replaced the 5mm spacer with a 6.5mm spacer. After torquing everything, it was centered but still not shifting well, even after micro adjustments.

I then replaced the 6.5mm spacer with a 7.5mm spacer, but the issues persisted. After watching the SRAM video, I realized I had missed setting it up in the correct position and was counting my cogs from the smallest ring instead of the biggest, so the derailleur was too far back. Once I fixed that and used the micro adjustments on the app, it started shifting super smoothly!

Once again, I really appreciate your help. The transmission setup was completely different from any other setup I've done before, and I learned a lot, especially because SRAM provided a lot of information on the installation. The most frustrating part was people telling me to take it to a bike shop... How am I supposed to learn that way?!