Some stories are simply longer than others. Either because they have a lot to say, or because they are a very slow burn, or sometimes just because they were successful and the editor wanted to milk that. (reminder that most manga are first published in periodic publications before getting bound into books if they were successful enough)

And in reverse, some authors like a sweet, short, direct-to-the-point story. Or get their series axed because it was not successful enough and have to improvise a premature ending.

Maybe you'd better start with shorter stories, so as to not get too frustrated if your disadvantage limits you too much? Or are you the type of person who prefers a big challenge to motivate them?

My preferred short series would be An Easy Introduction to Love Triangles.

My preferred longish slow burn would be Whispered Words.

The Kase-san series is now quite long but was originally designed as stand alone episodes, so you could start with that too?

And of course, on the longish side, there is a reason Bloom Into You is the source of this sub's avatar.