Yeah, fictional romance is more interesting when it’s forbidden in some way. Otherwise, who wants to read a romance novel about a nice couple who meets at the library when they’re both single, and proceeds to have a wholesome relationship? Great for real life, but boring to read about or watch a movie about.

Many of the traditional reasons for forbidding a romance are gone in the contemporary world. Different race, different social class, same gender, rival families? Not convincing.

So you’re left with stuff that’s plausible but icky, like being in a relationship already, or being teacher/student or boss/employee. Or pornographic stuff like step-family. Those are problematic and people will criticize them.

You could set your story in a historical setting in which the countess and the gardener are truly forbidden from passion, or a fantasy world where the ogopogos and sasquatches are sexy rivals.

Or just have a lukewarm type of forbidden-ness, like “his family’s greeting-card store is in competition with my family’s greeting-card store” or “we’re coworkers.”