How does tax work with crypto Debit cards? There are plenty crypto debit cards, like Crypto.com's or Binance's. I can easily use my fund to purchase goods and services without taking profit out of an exchange, and just simply use the funds on it.
If I purchase coffee with a debit card like that, is it taxable?
And if it is, how do I even know or calculate my taxes?
Is there a specific rule on this in the EU?
Is there a specific rule on this in the EU?

According to https://nomoretax.eu/bitcoin-taxation-developed-countries/

The fiscal treatment of Bitcoin for tax purposes differs depending on EU country.



how do I even know or calculate my taxes?


By consulting material published by the tax authorities in the country in which you are resident (and US as well if a US citizen resident outside the US).
By consulting a tax adviser.
By contacting the local tax authorities and asking them for advice. (In my country at least, they are friendly and helpful to people seeking advice).