There are some manga I wish were more talked about but they keep slipping under the radar. They would be Twin Star Exorcists, Seraph of the End, and Blue Exorcist. Why aren't they talked about more?
I haven't read Seraph of the End, but I read through 50-ish chapters of TSE and read through everything that the anime covered of Blue Exorcist. TSE wasn't really my cup of tea, and Blue Exorcist was alright but didn't stand out to me that much.
I did encounter quite a few fans of both online a few years ago, but I haven't exactly followed the status of their popularity or level of discussion since I stopped reading them. If I had to guess, though, battle shounen is a very saturated genre, so I suppose with so many hits coming out in recent years they kind of got lost in the shuffle among their contemporaries, even if generally well-liked by their respective (albeit niche) fanbases. It's actually not that uncommon. The same thing happened over a decade ago to series like Psyren and MX0, despite having a passionate following by their internal fanbases. Those two saw early cancelations in fact, so at least with those other two series they are still doing well enough to go on, which is always a good thing for fans.
Honestly, though, not a lot of modern manga get a whole heap of discussion these days unless they get a really strong anime adaptation to promote them. I was a fan of MHA and KnY from very early on, and I can assure you that discussion on both of those series exponentially increased after the first few episodes of their anime adaptations caught on. The KnY reddit membership increased multiple times over practically overnight with the airing of the first season. You can add Doctor Stone and TPNL to that list as well. If the adaptation is average or sub-par, though, then it doesn't really do anything for the manga's popularity. World Trigger and Hinomaru Zumou are primary examples of this, despite both being excellent shounen manga (IMO). I feel that TSE and Blue Exorcist fall into that category as well, as neither of their adaptations were particularly impressive in any regard.
I assume that sort of popularity boost will happen for other series with a strong following if they get similar quality promotional treatment, like with Chainsaw Man's upcoming anime. Kaiju No. 8 also seems like it could be a popular series with a high-profile adaptation a few years from now. Hopefully Spy X Family can get a good one as well, though with it's release schedule it'll be a while before it has enough material to properly adapt into a full season.