I'm not involved in art at all however you seems to not be alone at all; take a look at :
- https://www.bbc.com/news/health-47830256 - Aphantasia: Ex-Pixar chief Ed Catmull says 'my mind's eye is blind'
- https://www.youtube.com/watch?v=ewsGmhAjjjI - "an artist that can't see pictures in my head"
- https://aphantasia.com/article/strategies/how-to-make-art-with-aphantasia/ - How to Make Art with Aphantasia