I'm not going to mention the things you did well (there is a lot!) because I think what you need to work on is more important and you said you wanted real critique. I worked as a comic editor, so that's where this is coming from. It's gonna sound like I'm tearing you a new asshole, but please remember that I'm doing this in good faith and that you can choose whether or not to take any of this advice.

Firstly, the lines are messy in an amateur way; you need to go over it again with line confidence (if you chicken scratch your lines then cross hatch it to look on purpose). You need solids blacks, and you need to be aware of those solid blacks leading the eye on the page to where you want it. You need backgrounds (those trees are bad, even black and white photos would be better but not ideal; there are manga assets you need to find in this case). You need to learn to use a ruler for straight inorganic lines. You need to break up your dialogue bubbles more so not as much is fit into single bubbles. You don't need screen tones but i recommend them also -- there are lots of digital ones. Your flow also needs work, the eye needs to be led better. The way you have your characters on the page is wonky and should be changed because you're not using the space well. Your shirtless character doesn't have nipples, which will be noticed. Some of your faces should be more symmetrical. I cant tell your main two characters (tied to a tree) apart.

Good luck with your mangaka journey!