Usually it doesn't matter what you earn, as long as it has a value it's taxable. Even if you're paid in potatoes.
In practice it's not possible for them to find out as long as you didn't cash out at least once (and created a connection to your identity), but once they know they'll want their share, and might even fine you for not reporting in time.

Best advice I can give you is to ask a local accountant/tax advisor. There are some exceptions to what I said, Portugal for example only taxes crypto when you cash out - but all other (western) European countries I know about do tax it the moment it hits your wallet.