https://www.mangago.me/read-manga/struggle_1/
you lost me at "not posted here" but take a look at this..it's kinda similar to what you described
In the list of someone they posted a link to the story to a different webpage I meant, anyways thank you tho
https://blackbox-tl.com/novels/pm/pm-chapter-1/
I think I found it
title: Perfect match
Not what I was looking for but thank you for a new recommendation
I remember there was this webtoon styled art story and it was an omegaverse, it's not a webtoon posted here but in the beginning of the story there was a flashback of an omega and an alpha in high school doing the nasty and the omega was impregnated but the alpha seemed like he didn't want to take responsibility but years later the alpha looks for the omega, I remember it was on a list but I didn't follow it :/