How does the tax office find out if something is not taxed?

E.g. Twitch donations. How should the tax office find out that they are not taxed.

Related to Twitch: When someone doesn't like you and whistles at the tax office

First and foremost, it is a fraud against the community as you are certainly also taking advantage of the convenience of society. So it is a completely immoral approach you are thinking there. Furthermore, your user data is stored and can of course be used by the responsible authorities for a tax audit at any time if there's any suspicion. And then it gets expensive if your bookkeeping is wrong. Depending on age and other income, the legal allowances are not even low. But requires a proper tax return. Remember one thing, there's no quick money through tax evasion, you only get the ticket into crime.

Find a good tax association or tax advisor and nothing goes wrong.

In which the tax office responsible for twitch checks who has received all the money via this platform. The result is then forwarded to the local responsible tax offices of the recipient, who then check whether the income has been stated in the corresponding tax return