ohh lots of lovely art! I've also struggled with mental health. It's really taken a toll on my motivation to draw and I've put it on the back burner for the last few years :( The main thing to keep in mind is not burning yourself out. Take a little time out to focus on drawing what you love without all the do's & don'ts of the art world. I expected too much of myself and when things didn't pan out the way I expected, I just didn't want to do it anymore. Looking at other artists have been super inspirational for me though!
Most recent piece - This is amazingly detailed wow! The dress could use more contrast to help define the folds and bring more shape. I'm not sure what type of pleat the skirt is, there's a lot going on. Cleaning up the lines/rendering that area more could help with that. Something else I notice is her shoulder area. The small lines you have tapering inside, towards her chest is awkward. Having a line tapering outwards from her armpit area will look more natural. Brass and jewels are a bit tricky since they require a lot of contrast. You already have a good hand for all the tiny embellishments! I recommend avoiding black for the shading and try using burnt umber, reds, and oranges. This will not only add more contrast but make the piece for vibrant! Lastly, the middle of the bow on the staff is missing, not sure if that was intentional?
Most varied - A good way to explore different styles and experiment :) I recommend using a thicker line for the lineart. If it's too thin, it starts looking pixelated from a distance (like this). Using thicker line art will make it look cleaner and add definition to the piece. Play around with different sizes, even varying the thickness within a piece can add texture and character!
Most popular - This one has good contrast! There's some great movement, particular in the girl to the left, that adds energy to the piece. Now there is a little confusion in the light source. Their skin and clothing seem to have a light source coming from the right top corner while their hair has a light source coming from the left top corner. I recommend putting a marker where you want the main light source to be as a guide. A little nit-picky thing is their skirt/pants. The left girls skirt could use a darker shade for the lineart to add contrast. Right now, it's all blending into each other, losing a lot of movement in the pleats. Same with the right girl; her shorts are a completely solid black. Since it's a high-contrast shade, it causes the skirt to be the main focal point in the piece and lures the eye to look there first. This doesn't seem like an important thing but you want the viewers attention to go to the most important part of the artwork first, before they start looking around at everything else. Basically, first impressions are important! You can still keep it a solid black if you want but you can also add some light highlighting. I've also seen artists add extra lines to hint at and separate different pieces (like this in one of my artworks).
WIP sketch - Since this is a wip, I won't say too much! The legs are a bit awkward. I have a hard time with positioning legs, I understand the struggle ; n; I think the problem is they're sticking too far out. I tried looking for some references for ya that are similar~ one two three
Overall, keep doing what you're doing! You already have lots of potential. There's always something to improve on.. I've been drawing seriously for roughly 11 years and I'd say I still got a long way to go. It's a never-ending process to be honest haha. I'd help more with perspective but I don't have much exp. with that yet;; Hands are the bane of any artist lmao. I could write more about those suckers than anything else. But I won't word-spam you, unless you want it.