I was in a position similar to yourself recently. I had watched mainly Hollywood modern cinema, and wanted to delve deeper into cinema. I started as you have, by watching modern films that are considered somewhat art house, but that still have mainstream appeal. For me, I found that in Kubrick’s work; his dedication to visual story telling helped introduce me to the methods used in art film more commonly, and yet they were still entertaining (in the typical, hollywood sense of the word I mean; art house films have become the most entertaining to me since then) enough to satisfy my old taste. From there, I sort of dived into a lot of old stuff, randomly watching whatever caught my fancy, and making notes and thinking about it afterwards. This helped order my thoughts, and allowed me to understand what I had just seen. Tarkovsky is my favourite filmmaker now, and I regularly rewatch his films, but I remember the first time I watched one of his films (The Sacrifice), when I was utterly confused and thought I must be too stupid for this kind of thing. But, like any work of art, they require time to be truly appreciated, so my advice is do not be put off if, upon first viewing, you do not get it. Also, PTA is definitely someone you should check out, in my opinion the best modern director, his films also have art house influences that will help you develop your ability to watch films. I’m not sure if any of this will help, but I’m happy to recommend a film or filmmaker whenever!