For starters, due to their own policies and ToS, when you create your Patreon account you must indicate you're creating +18 content. If you fail to do that you can be deplatformed as you were lying to Patreon about your creations, so don't do that. (BTW, DarkCookie's patreon is rightly labeled as +18 and you're asked to verify your age when you try to enter it without being logged, as it should be).
That said, I don't know how a Patreon's receipt looks like, but it will probably link somewhere your real ID to your Patreon's account. This could be easily confirmed just by asking some active dev. Does it mean your tax agency can snoop around to find out what are you offering in Patreon? No... unless you're under investigation. So yeah, they could eventually find out, but anyway they don't know you personally and no one is going to use that info against you - at least, not in a decent country with a non-totalitarian regime, so probably there's no need to feel ashamed. Now, if you still fear this info could be unveiled in the context of a legal process because you somehow broke some taxing rule, thus causing you some personal problems, then yeah, your fears are justified. It will happen.
Then, the tax part. You really should look for blogs or forums specialized in your country's tax system and ask there. I'm sure there are a quite a few, as taxes are one of the hottest topics in the net. I know in some countries you just need to say how much money you earned from this 'extra' activities and not what those activities actually are, but usually this changes depending on the amount (sometimes if you earn more than a certain hard limit you must be registered as a profesional even though it's not your main activity, sometimes when those incomes reach a certain % of your total income you need to provide some extra information about them...). As I said, ask in a specialized forum in your own country, you'll surely get better info than here.