I keep seeing a lot of lists that throw around the same few titles, but honestly, 'Ascendance of a Bookworm' gets the romance angle so wrong if that's what you're after. The main drive is the protagonist's obsession with printing, full stop. The romantic subplot is glacially slow and almost an afterthought for many arcs. It's a fantastic series, but if someone sells it to you as a romantic isekai, they're setting you up for disappointment. You'd be better off with something like 'The Saint's Magic Power is Omnipotent'—the romance is central to the plot, not just a vague possibility on the horizon. The female lead's relationship with the knight commander develops with a clarity and purpose that feels integral to her new life.
Another one that handles romance as a proper subplot rather than just fan service is 'My Next Life as a Villainess: All Routes Lead to Doom!'. The comedy comes first, but the protagonist's genuine, clueless bonds with all the capture targets create a romantic atmosphere that's surprisingly sweet. It's less about choosing one person and more about the warmth of all those relationships, which I find more engaging than a typical harem setup. The light novels expand on the game's lore and character motivations in a way the anime couldn't fully cover.