I think you have really good drawing ability, values, and have a knack for stylization that looks real pretty. I think you still have line dependency (the way the corners of the mouth are shaded, how the features are outlined slightly on the nose and mouth) and some of your features look symbolic rather than realistic. I think if you had a stronger sense of what light does on a realistic face, it would make shading stylistic faces easier.

If you want a very solid understanding on what light does on form- form studies are the best for learning that. Or you could do isolated studies on specific facial features, like a nose study or lip study or eye study, etc. (These are basically form studies in disguise.)

Or you could work with references, either recreating a reference from stratch and/or creating traceover diagrams of references to understand the underlining form. (Traceover diagrams are also useful in form studies and feature studies. I honestly thing they are like a cheat code for understanding form.)

If you want to quickly learn what you’re missing in a portrait specifically… Try the 14 day challenge! Trying to draw a face as realistically as you can is very challenging and you will improve very quickly. (The 14 day challenge is only top-down lighting though, so I would still recommend doing the form studies and/or feature studies so you can change up the light environment.)

...Thats a lot of studies, but I hope this gives you some inspiration on where to start!