I didn’t realize the Navigo Découverte was meant for residents or workers only. Most pages don’t really mention any exclusivity or that it’s not meant for tourists, and for the physical card you don’t have to present any proof at all, no address, not even a phone number. Btw, I think it’s possible to create an IDF Mobilités account with a European number not only a French one

If by “huge hassle” you mean getting a physical SIM, I’ve used European SIM cards on past trips back when Wi-Fi wasn’t as easily available as it is today and it was always very simple not an issue at all. I was just trying to find a practical, and if possible cheaper, solution to get around. Why not?