Money laundering is covering up illegal profits. Income from trading crypto or crypto capital gains are not illegal.

https://en.wikipedia.org/wiki/Money_laundering

So this is not money laundering.
You probably could use the proposed solution to do money laundering if you were receving profits from something illegal and needed to show legal profits instead. But this is not the case discussed here.

'but receiving EUR 90k,- worth of income from the UAE for a property that is worth EUR 1k,- in rent may raise some eyebrows and trigger some deeper investigations.'

I know a person who sells a product to his clients that he actually receives for free. It's not a sin to sell something with a high markup.

Also from the perspective of your tax authority the rent received is taxable in the other country (UAE). So it is not looked at as being 'taxfree so it has to be suspicious'  but as simply 'not their business'.