I totally understand where you are coming from - I started Stan's anatomy course about a year and a half ago and I got through bones and sort of lost the will to live on the muscle bits because I couldn't visualise the muscles from the outside... I had some time off, and have recently been watching different videos that concentrate just on the head or just on the hands - and I find that focusing on a single body part makes it feel more manageable. I have to admit I have found some of the resources on the New Masters Academy website really useful - drawing skulls and cadavers with various bits cut out - sounds grim I know, but its pretty interesting when you get into it - the difference is that you spend more time on single bits so it all moves more slowly and you start to feel more comfortable and familiar with one set of muscles before you get onto something else - I'm posting my cadaver sketch of deep facial muscles so you can see the sort of approach in case you think it might help

my advice to you would be to diversify your resources. A lot of anatomy is just as much about how familiar you are with your subject vs the drawing. A lot of people approach anatomy differently, so it could be helpful to keep watching videos of people talking about anatomy/their thought process while they're drawing. That could help you know how to decide what to learn next

I think the 4th drawing is actually starting off pretty well. When I get stuck or frustrated with a certain pose or feeling like I'm lost, it's usually an indication to simplify and go back to the basics. So for example with the 4th drawing, looks like you were pretty proficient with placing the chest and shoulder muscles, I can see where they connect to the skeleton and the forms look good. Then as you moved towards the arm it looks like you were a bit more uncertain and that's also where I see less "construction" and the sort of deliberate placing of muscles. I would recommend when you can't seem to understand the reference to draw out the primary skeletal forms and then connect the muscles where they are supposed to connect. So: 1. look for the boney landmarks on the reference (sternum, clavicles, elbows wrist, etc. basically those boney landmarks that you can see on most people), sketch those in with very basic forms, then 2. connect the muscles to those landmarks. I know that sounds over-simplified, but really those 2 basic steps should get you there. If you connect things correctly it's almost like you can't get it wrong. If you knowledge is getting jumbled, just take a break and review that specific part, that you are stuck on, ask yourself: where should this muscle connect? Once you have that in mind, you'll likely start seeing indications of the form in your reference. Where you can still go wrong, is not understanding how the form changes with perspective. What helped me with that is doing some basic 3D sculpting and really understanding how the muscles connect in 3D. You aren't going to get super clean drawings right away, you'll have to go in and erase some of the under-drawing, but over time you'll need the under-drawing less.

Paul, I'm just a novice and unfortunately I can't give u a professional critique. But I can say that I really like your lines and the proportions look very good to me. Now about your question... well I think I know what you mean and I understand your feelings because I feel the same any time I expect some feedback from an instructor or at least from a senior artist with more experience than me and nobody respond. This is the weakest point of this platform and his community. And I told Stan in a video chat we had some months ago when I was requested to be a beta tester. There is no structure here you can find in an Art School instead. I know. It's frustrating not to know if we are going in the right direction. But I can also say that if I compare my works now with what I could do a little more than a year ago when I joint Proko the first time (29 Nov. 2020), I can see a dramatic difference. I improved a lot. Thanks of course to my constant daily commitment. But also thanks to the contents that Stan and Proko's Staff provide. Video are funny, very easy to understand and based on years and years of teaching experience. I learnt about perspective and anatomy, colors theory, lights and shadows, composition, etc. In the end what I'm trying to say is that mastery takes years, decades. If we want to become good there's only one way, Practicing, studying, making mistakes, fixing them, repeating. And don't lose a chance to show your works to other people. Here and outside the community. And if you can take some lesson periodically in an atelier or some sort of art school (even course for amateurs) it would be great! Good luck!