I've been drawing pictures and publishing them as desktop wallpapers for ~20 years now, selling Vlad.studio accounts with unlimited access to downloads [0]. In 2021, I earned $4761, which means ~$400/month. It's not horribly little amount, especially for Russia (where I live), given it's a side project. However, I feel I need to do something more active, rather than just drawing new pictures. Promoting and marketing…
I mean it could go either way, just make sure you also consider the upside of a fun (slowly / organically growing) side business.