Okay, let's see here...
Overall this is actually a pretty polished comic, and I'd by no means call it "bad" by any stretch!
The text is definitely too small for mobile (nice fonts though), and should be at least 1.5x the size it is now, honestly 2x might even be good, and the speech bubbles are very cramped, so here's a tutorial to get that fixed up.
The art is honestly pretty nice, with a confident, consistent style and really good palette. The figures are well proportioned and the poses tend to read well.
There's a bit of a weakness in the way the figures are interacting with the environments. It often feels like rather than standing in a place, the characters are kind of floating in front of a place because the perspective and angle doesn't quite match. Maybe take a look at a book called "Perspective! For Comic Book Artists" by David Chelsea to help with that.
The backgrounds are sometimes a bit on the dark side for how dark all the characters' outfits are. I found myself squinting a bit to make out the characters from their environments at times. Try to add a bit more contrast and tonal variety to the pages.
Finally, honestly webtoon is a bit of a mystery to me and what's popular often is a bit random and dependent on gaming canvas days. Why not try fixing the font size while saving out the pages at 940px wide, making a really nice cover and uploading here on Tapas? With the quality of this comic, it could well get a "New On Tapas" feature, and I feel like the vibe and style could potentially fit well on this platform. Worth a shot!