You've met in person, which is the main requirement. Don’t worry too much about not having many photos, what matters more are things like flight receipts, hotel bookings, and consistent chat history (even if it’s all on one app).
A past tourist visa denial doesn’t automatically hurt your K1 case. Just be honest, document your relationship well, and include letters of intent to marry. You might also find this Argentina tourism guide helpful to understand how your country is generally viewed in the travel context https://gowithguide.com/blog/tourism-in-argentina-statistics-2024-a-comprehensive-travel-guide-5706
Everyone’s situation is different, what matters is that your relationship is genuine. Best of luck!