Well let's hear it then, give me a list of every page you thought had a joke/something funny on it in this series. Show me the "humor" and explain why it's funny to you. I'll be surprised if you can even point to more than a couple that aren't complete "how the fuck is this funny" moments.
There's tons of examples of irony mixed with tragedy through out the entire series, but I'll just stick to one and try to explain it in depth to where you might finally get it and stop complaining about something that obviously isn't for you.
Teru is the usual best friend character being fucked around with to its absolute limits. Trying to find his "Girlfriend" Karagaki, going through the stages of grief being the only one caring that she was gone despite it not being really that well reciprocated to what we know of so far. He beats himself over it for multiple chapters even after confirming she wasn't faithful. And going to his best friend the MC who is partially responsible for her disappearance, and them having a best friend moment as he stands over the bridge. And ironically almost moves on instantly to an older woman who gives him a bit of attention, even if he feels guilty about. Only to get cucked over the phone while trying have another friend/relationship using his dead girlfriend's disappearance as an excuse which the older woman saw right through if you paid attention while immediately after have his mother leave him. Which then makes him kill himself.
Only to have that whole arc immediately undermined by the fact Karagaki is then revived right after his little arc is concluded. It's tragic, surreal, but most importantly extremely ironic. If she had been revived a earlier Teru might still be alive with a sweeter and kinder version of Karagaki. But no she goes back to school and this clean slate takes the torch of Teru's suffering in what guessed to be now her own arc. The humor is extremely light and can be overpowered by the just how absurd and dark the other material is. But that's what still makes the humor noticeable how absurd all of this is, and how it is played straight. Hell another example of something dark with a somewhat unlikeable protag is Death Note. Popular for how straightforward and non-gag oriented its comedy was. Hell Fujimoto with his entire discography is famous for it.
There are tons of old literature that teeter the line between tragedy and comedy (Divine Comedy). Hell theatre does this lots of times and even has a symbol that reflects this. If you don't like it or think it pushes too far in one direction for you to find it funny that is fine. But with the way it's illustrated the author obviously wanted some of it to not be taken seriously or at feel surreal. I could name other examples but honestly why bother it seems like you and
Jackist are adamant about your stances on what counts as acceptable art or comedy and at this point I feel like trying to teach you both the history of writing and how even dark humor has been used to cope or even entertain through hard times would be lost.
Personally I liked Teru as a character and feel he got a little too much hate in comparison to the literal cheaters, murders, and accomplices in this manga. But what can you do? People hate "simps". Guess it's heavy projection.
