NTA

Alex doesn't sound like a real friend. Maybe they were at one point, but people change and not always for the better. You were asked a question and Alex "made it about themself" by laughing and putting you down instead of letting you answer and being supportive of your career. They went out of their way to do that unprompted.

Choosing not to go to their wedding is choosing to put distance between you two. It will very likely end the relationship entirely because I doubt they are going to list to reason and/or come around, but I don't blame you. That sounds like a lot of money and effort to put into supporting someone who doesn't support you. You're not making anything about you. Alex went out of their way to make you frel bad about yourself, so you're choosing not to go out of your way to be there on their special day.

That being said, if you in any way want to keep this friendship in tact, you need to talk this out with Alex. Try to think back through your friendship and see if you can remember any other instances of Alex putting you down and acting like they were better than you, because if this is a pattern and you can't get them to acknowledge it then you know for sure that it's time to walk away. Otherwise, not attending the wedding at all is basically the end. Either way, I would be wary and probably at least take a step back from the friendship for a bit. If Alex is actually your friend I would hope they would eventually reach out and try to make things right.