Ugh... it's hard to find underrated novels that are good and focused on the yandere part. I've also forgotten some of them already. The one that comes to mind is:
'I Got the Hypnosis App, Now I Can Do Whatever I Want!'- it's pretty good
'Oh no! After I Reincarnated, My Moms Became Son-cons!'-I remembered feeling uncomfortable while reading it because of the mc so I dropped it halfway but it was yandere
'Running Away From The Hero!'- i think you already know this but just in case, I will recommend it too.
I'll also give you a harem novel that I'm enjoying right now:
'Stealing the Yuri Protagonist Harem'
'Reincarnated in The World of a Yuri Game as a Man Who Got Sandwiched by Yuri'
'The Main Heroines are Trying to Kill Me'.
