As you are unable to earn income, perhaps you can report the royalties on Form 1040 as just that: royalties. It is questionable whether the receipy if royalties is self-employment income anyway.
It’s not at all questionable whether writing apps (or novels, or music) for profit generates self-employment income. There are other things called royalties (an inherited right to receive income from a decedent’s writing activity, or the right to receive income from someone else’s development of your mineral interests, for example) that are not self-employment income. The OP does not have the second kind of income.
OP, you need legal advice. You also need to stop incriminating yourself in a public forum.
It is questionable. Rev. Rul. 68-498. We don’t know the facts. We certainly can’t give OP advice either way.
^True - though OP did says “apps” (plural), and not one app so as per the 1968 Revenue Ruling you cited he might be regularly engaged.