I've experienced this in Indonesia, China and the US.

In Indonesia at least, even if they say they don't accept it, if I gave exact change (plus a little extra at times), they STFU and took it.

If they pressed and I'd given exact change, I could literally say, "you scan that QR then for me and take the cash".

I'm surprised legal tender laws don't protect the right to use cash... Insane. (edit: I don't like legal tender laws BTW, but still... In this case it should mean you can spend your money ANYWHERE even if it's cash)