Earlier quoted context omitted.
Pretty trivial for a nation state, given sufficient motivation.
Not if it's something like Monero.
If you're making a lot of unreported income, there are ways for the tax authorities to know, in the same way they do with income from illegal activities that you're not reporting or large amounts of cash payments you're hiding, or just unreported income in general.
They don't need to match your identity to your Monero addresses. If you're using your Monero in any way that interacts with the real world they're going to ask where the money in your accounts came from, where the money for these assets you've been buying but don't seem to have a way to afford came from, where the money for these investments you've been making came from...
Even if you can somehow obtain things without converting out of the cryptocurrency, you're still acquiring assets, investments, and the like that require registration and disclosure, which will then lead to the same questions. Paying your monthly rent directly in cryptocurrency? If anyone audits or investigates you're going to have to explain how you're affording it when your reported income doesn't seem to support it.
And the sellers/landlords/etc will themselves have records, so you better hope they're also completely committed to protecting you if they themselves get audited or investigated.