For starters, my impression is that American Express is a great place to work. I had a great experience actually going to my in person interviews and meeting various members of the team. That said, the recruiting team is a mess.
I've applied and interviewed for 3 positions recently, and every time I have worked with a recruiter they really dropped the ball on communication. Multiple times I was given a date I would hear more, and multiple times I never heard from them. Multiple times the recruiters excitedly stated "reach out at any time with questions!" and then ghosted. I have spoken with people inside the company, and they have repeatedly apologized for the recruiter team and suggest I contact the hiring manager directly if possible.
My advice: if you have multiple offers, do not wait around for American Express.
Interview process itself was fairly standard, though inconsistent. Some positions have a phone screen, some combine the technical/behavioral interview, and another separated the technical and behavioral. One position I was told the time for a decision would be a few days after the interview, another said it could be multiple weeks or longer.
Technical questions were entirely based on what I put on my resume, and fairly consistent with other reviews.