I just wanted to give an update on some things related to the experience.
1. On the Facebook group some people were freaking out about their interviews being cancelled because they had travelled in the previous 14 days. We did not see this until after my fianc came to the US for her vaccine and went back. She got a negative COVID test in hand just to be safe and hedge bets and in the end they have things designed so you are never face to face with anyone (bank teller-style booths) and never mentioned anything about COVID.
2. On the instructions they ask for the petitioners birth certificate and then the birth certificate OR US passport. When she went in the day before to turn in the paperwork she was given grief for not having a copy of my passport. I quickly got her one for the actual interview and they didn't care.
3. They don't seem to understand how originals work, but that doesn't seem to make a difference other than their attitude. If something is digital, bring in two copies (even though they are identical) and be prepared to explain that some places (such as Mexico City) are not providing non-digital original copies.
4. There seems to be a backlog on giving out visas after the interview, right now seems to be something like 7-10 days though we are still on day 8 of waiting so it could be longer.
5. The biometrics appointment was a huge PITA to schedule because there's some kind of disconnect between the embassy and the third party they use; you try to schedule an appointment and pay the visa fee and it simply doesn't allow you. It seemed like her record hadn't been updated yet in the right place for the 3rd party system to work. We ended up having to call every day for nearly a week before we got the right person who knew what to do to fix the issue.
If you have any questions I can do my best to ask my fianc and answer. Ultimately it is apparent that they are not used to this process and struggling a bit with it, but its awesome they've opened up in Mexico City because it's pushing things through a lot faster as a result for K1/C1's I think across the board.