Yeah so.. hands are just hard. lol.
First: It's kind of dependent on the situation how much structure and detail you need to implement in your hands. Study is important but the more understanding and skill you gain for hand drawing the more niche the situation in which you need all that becomes. Don't stress too much on having it all down. Think about the situation you'll be showing hands most in (manga comics, animation, realism etc.) and focus on finding a solution that carries you well in that space, then build your hand drawing skills over time from there. As with all figure drawing, it's a life long journey.
This example you provide is already very impressive and shows you know how to break down the larger gesture and have a basic understanding of the anatomy underneath. That goes a long way with hand drawing in most scenarios. From the character peaking in the background I'll assume we're working more stylized usually (or at least that's the end goal) and so my advice to get you moving forward would be; simplification. Make the approach as simple as possible for yourself.
Take examples of artist styles you like and do studies- break their hands down into simple cylinders, spheres and cubes. Do the same with references of real hands until you kind of pick up you own "shorthand" (pun intended) for how to lay in basic structure and get the style you like. Do that until you land on something you like and doesn't make you scream and you're in business!
phew, hands are a lot to talk about! sorry about all that reading.
Looks like you're having fun! You've got a lot of mileage and show a solid understanding of anatomy, gesture, line control, etc.
I would recommend slowing down. You seem stuck to what you see. Let yourself digest the information and marry what you see more with what you know. Slowing down and starting with a less chaotic structure you can add clarifying secondary shapes in addition to your bony landmarks and muscle outlines. You clearly already have a lot of knowledge in there: now you can step back and use it!
