Please don't pay taxes on your coins.
You really don't need it, unless you are totally ignorant.
It's simple: they cannot prove you have the coins on your PC/phone , so you don't have nothing to pay taxes on, as far as they know.
It's just their attempt to trick the ignorants that don't know about that
Even if they look for your wallet on your PC/phone ,
your wallet data is not accessible to them because it's encrypted with password ( uhm.... have you set the password protection on your wallet... right? ).
Of course you are not going to give them the wallet password.
Oh.. they tell you that you withdrawn the coins from an exchange, so that's the proof you have the coins?
Just say that it was an hacker that stole your coins from the exchange, not you.
You got robbed, and you don't have to pay taxes on the money that was stolen from you, right?
P.S. for the geeks: use Veracrypt
Is it just because paying taxes with crypto assets has such an impact?
I don't think that's possible, what about those who use crypto assets to shop, isn't that the same, the only difference is the name of the platform?