You might try different media if you haven't already, as in, instead of pencil/pen and paper, maybe colored pencils or markers. Maybe even try getting some black paper and trying to draw with white color pencils instead.

I'm sure you may have tried a variety of things over the years, so I'm just spitballing, but also if you're trying to dive into the deep end with more complex drawings, you might revisit and really hone the fundamentals. Fundamentals being like getting clean lines by practicing drawing those over and over till you can get a nice, sharp line (which often isn't a single pencil/brush stroke!).

Once you have those down you may move on to the simple shapes, squares, triangles, circles, and try to recognize how those are put together for more complex forms. It's a tough skill to get down, without a doubt (I'm not some proficient artist personally), but it's just that: a skill that takes not only practice but learning methodologies. One of the toughest parts with drawing is that there's so many methods to go about it to figure out which helps you improve.