Book where the MC is hated for a reason? (With no romance as the focus)

Speaker For the Dead is kind of like this. The MC is hated for actions taken in a previous book (Ender's Game). That said, the main character travels under his real name as opposed to the pseudonym he was known under when he did the things that made people hate him now. Also, due to time dilation from traveling at near light speed, his actions were ~3000 years in the past. As a result, he is basically a mythical evil figure in the general consciousness, but is not hated in his day to day life because people don't know who he is.

Not sure if this is close enough, but it is the only thing I could think of.

I Am Legend?

An obvious one might be Rand from Wheel of Time series. He is feared/hated by various groups for various reasons. One of the biggest reasons is that he is destined to break the world again. The Aiel especially have a weird relationship with him because of this.

Lord Foul's Bane, by Stephen R. Donaldson. The main character is transported to a mystical land and one of the first things has does is rape the young woman who summoned him. The repercussions last literally for millennia.

In the Scholomance series, the narrator has this curse of unlikeability over her. But she decides to fully lean into it and is an absolute jerk to everyone, and it's pretty glorious to see her being so freaking rude to the few people who actually want to befriend her.

Greener Than You Think by Ward Moore.

It's a satirical science fiction novel written in the 40s that, aside from the dated cultural references, might've been written today.

The MC and narrator is a salesman who answers an ad wanting someone to market a product that will make it so that plants can extract nutrients from virtually anything. The woman who created it envisions people in even the most barren areas being able to grow food regardless of the quality of their soil, but the MC believes that she's just a dumb woman who doesn't understand business, and obviously those people couldn't afford to pay enough for this product, so the better idea is to market it to suburban homeowners to put on their grass.

Which leads directly to the entire world being overrun by an unstoppable mutant strain of bermuda grass.

Throughout the entire chain of events, the MC remains completely oblivious to the threat facing humanity, and is instead entirely focused on profiting off the events. He's like every self-absorbed politician or corporate executive rolled into one, overtly bringing destruction to countless people in his blind pursuit of profit and privilege, and railing against anyone or anything that stands in his way.

And naturally, the people he meets pretty much universally loathe and detest him. And if he notices it at all, he ascribes it to their purported jealousy or envy or ignorance.

Consider Phlebas comes to mind

Most readers agree that the MC of the book is not a good person. He's fighting a war on the side of the Religious Authoritarian genocidal slave drivers, just because he doesn't like the fact that the other side (who are fighting to stop the whole galaxy from being conquered by these asshats) is essentially run by it's AIs. And he goes to extreme lengths to continue to support his shitty masters, betraying people who come to trust him, and just generally being a bad person. It's an interesting read, because the whole book is told from his own perspective, so the fact that he's a terrible person isn't really spelled out for you, all his actions are presented (in his own mind) as totally understandable, and even heroic.

There is a romantic subplot (two, technically), but it's definetely not the focus, and can honestly be ignored for the most part if you're not into it

Imperial Radch comes to mind. Really, a lot of military-focused genre fiction has shades of this. Black Company, Malazan Book of the Fallen, Old Man's War, and similar tend to have main characters that aren't exactly loved outside of their in-universe group. Someone else mentioned Consider Phlebas from the Culture series, but Use of Weapons is another stand-alone from that series that might be worth reading if you're looking for a main character who is hated for a reason.

I know it's not quite the same, but Song of the Beast by Carol Berg is kinda like this. The book starts after the main character is released from a 20 year prison sentence and he's trying to find out why he was in there in the first place

Not quite what you're asking for, but Dalinor in The Way of Kings is at the very least distruted by his peers and hated/feared by the non-Alethi. He's not hated by most of the other main characters though, so not quite a loner that everyone hates. We don't really know why at first, but it ends up being for quite a good reason, and definitely leads to drama and conflict, as well as character development.