You're absolutely right, cash is indeed inconvenient. But all digital payments make you pay a middleman "platform" which tries to extract as much of the transaction as possible while providing the minimum possible value. Oh and by the way this platform's also trying to become a monopoly so it can eventually provide less than the minimum value without losing you as a customer.

Crypto claims to be a solution to this, but in practice approximately all crypto transactions go through a middleman (exchange) which takes a cut. It's unreasonable to expect your barista to go through the effort of accepting crypto payments without involving an exchange.

Cash doesn't have this problem.

I'd love to be proven wrong about this. Is there a digital payment method that runs on phones that doesn't subsidize a middleman?

Chinese payment platforms are the closest to a light middle man, but this might just be VC subsidizing things. Cash has its own expense of course, you need a middleman regardless, even if it’s just your local bank branch taking daily merchant cash deposits.