The Verdict: Need More Info
Your route is the freelance permit, which turns on showing your work will support you in Germany. Gather letters of intent from clients in Germany and an income projection before you apply.
Section 21(5) of the Residence Act covers the liberal professions: doctors, lawyers, architects, engineers, journalists, translators, artists, teachers, consultants and much independent technical and creative work. Where the profession is licensed, you must hold the licence or have it promised.
No income figure is published, and expectations vary between cities. The strongest applications carry letters of intent from clients in Germany, a realistic income projection, health insurance and a record of doing this work before. If you are over 45 you also need adequate pension provision.
This permit is for work in Germany, not remote work for clients elsewhere. Germany has no digital nomad visa, and applications framed that way tend to fail.
The permit is usually granted for up to three years. Permanent residence for freelancers follows the ordinary route at five years, not the three-year rule for business founders.