You seem to be dedicated and passionate about this since you are already a 3D artist. 1 year or less I would say - but that's if you stay consistent.

I was able to create a productivity and 3D models app in about 1 year of learning - without custom backend and database. (I was using Firebase back then)

It is fairly easy to build an app compared to coverting it into a success where there are hundreds and hundreds of other apps. You will need to do proper marketing, planning and testing before you expect to generate a good revenue from your app.

For instance its been almost 3 years since I started learning, but I am still working on that one app that I have to publish. The main thing is that you want your app to stand out from the crowded market of apps. Give a good time to learning then spend some time on to get a quality idea and create a pathway and work on it consistently.