BTC to BTC transaction in the wallet are private. Once you convert, banks are involved. We report aggregates yearly (bitcoin bought, bitcoin sold) (see here: https://help.bringin.xyz/en/articles/15392537-what-data-is-bringin-required-to-report-under-dac8) So your final receiving bank doesn't know that Bitcoin is involved. But we do, and we need to report that when we report the aggregate. If it is or it is not a taxable event depends on the country, but generally speaking yes.