2 years ago, you needed Indian number to use UPI.

Took me 2 visit to fully setup. First visit to India, they are like I need a debit card. I hate debit cards, but I got it. Which got delivered to my US address. When I got there, they are like I need Indian number and I have to do KYC to update. 3rd visit, I got everything working. At that point, they also let you use US number. But I wouldn't recommend US number as roaming is expensive if you have ATT.

You also have to disable developer mode and can't root the device.

Impossible for tourists to use yes. You need an Indian bank account and there are services ostensibly for tourists but they still don't work everywhere, for example many vendors will want friend payments instead of business payments because they don't want to pay the surcharge.

Tourist UPI only permits P2M payments, and most normal transactions (as well as refunds) are conducted P2P.