That changes of course, but mostly in big cities' centers (Covid accelerated things in Berlin). I hope businesses catch up with the new wave of payment terminals like iZettle and SumUp - they support all these different cards without a problem
Where are you having trouble with AmEx?
Not sure how it works now if Amex has discovered chips and contactless. The payment processors probably still need a separate path for Amex and I haven't seen that logo in a lot of places that do display visa and mc. So maybe it's still only available in tourist traps.
Funny enough, loading money from my bank account into my Apple Cash which is VISA allowed me to use Apple Pay, avoid ATM fees, foreign transaction fees, and was just more pleasant than using my bank card.