Depending on how you look at it, this might be kinda the opposite of what you’re asking for, but I thought I’d throw it out anyway in case you may still be interested: The Ideal Sponger Life is about a Japanese salaryman who gets isekai’d (willingly and intentionally, for a change) and marries the queen of a desert nation who needs a husband for political reasons but is reluctant to marry any of her statesmen (again, for political reasons).

The manga/novel (hasn’t been animated just yet) mainly focuses on the political relationships between the nations of the isekai world, and the MC struggling to figure out how to reconcile his cultural differences while also being a decent diplomat for the sake of his nation and his wife.

Part of that is the fact that MC’s marriage was initially purely political, but he and the queen grow to genuinely love each other. However, polygyny is the common practice in this new nation, especially among aristocrats, so MC is basically required to have a harem of wives, even though he very much doesn’t want any other than the queen. This results in him having to find clever, politically acceptable ways to avoid advances from (shrewd, surprisingly well written) women who want to join his harem to garner power for their families.

In summary: It’s a political fantasy story that is only technically a harem, and even then it’s not ecchi/oblivious MC/blah, but an integral part of the political intrigue in the story. Don’t know if that’s still a deal breaker for you, but just give the first volume or two a shot. I went in with very low expectations and was blown away with how well the worldbuilding and characters were executed.