Amazon is doing its own fintech play here, with heavy investments into Amazon Pay, Amazon Credit cards, and more. None of that seems to be driven via Stripe, but other local partners and banks instead.
Maybe everywhere that accepts Apple Pay, but given how low credit card penetration is in Europe overall (relatively), it's almost impossible to avoid falling back on cash at some points unless you're very limited in the places you patronize.
UPI adoption is massive (and not just in India). The ubiquity of it is a huge benefit to the consumer - simply the knowledge that you can reliably depend on using it even for a random street vendor is a huge paradigm shift, compared to the status quo of knowing that it might be an option, or might not, depending on who you're talking to.
From a customer POV, UPI with it's lower success rates, no chargeback/dispute mechanism and with higher latency (take out your phone -> unlock -> open app -> click scan QR button -> enter pass -> Look at loader for 3-10 sec) is worse than debit card set up on phone / watch.