A McGuffin refers to a literary goal--such as the Holy Grail--which simply supplies the pretext for characters' actions. Nobody is quite sure why they want it. For all intents and purposes, it could be a Holy Partridge Feather since the goal is far less important than how the characters get to that goal.
Although most romances are not always as extreme as Romeo & Juliet, the goal of most romances is in fact to overcome differences or misunderstandings or tensions (of personality, social class, age, etc.) in order for the couple to get and stay together. Sometimes the goal is to overcome religious disparities/pressures. Those pressures supply the plot device that keep the main characters struggling until they understand each other well enough to form a unit.
A perfectly respectable plot, in my view.
It does help, however, if the religious pressures are MORE than a McGuffin.
A comparison between Love Means No Shame by Andrew Grey and the Gay Amish Romance Series by Keira Andrews points the difference.
I should say first that Andrew Grey is a perfectly respectable writer, and I quite enjoy several of his books, including The Best Worst Honeymoon Ever. In the case of Love Means No Shame, however, he might have been better served leaving Amish country alone.
The difference is the difference between a McGuffin and an actual setting/culture/milieu that informs the characters.
The Amish connection in Love Means No Shame is . . . well, there isn't really one except for a mention of "rumspringa" and Eli's clothes. And his feelings of shame. But really, he could be a traveling circus performer who abandoned his family or a cosplay actor who absconded with someone's lunch money or a freshman who dropped out of a college and doesn't want to go home and tell his parents. I'm not sure why he needs to be Amish--other than that the story takes place in the country. Maybe because Amish-romances tend to be surprisingly popular (like Laura Ingalls Wilder tributes: all that wholesome living without pesky things like grasshoppers and disease and freezing to death).
Keira Andrews's series, on the other hand, is quite good and quite fascinating. For one, she closely researched Amish communities, coming to the obvious conclusion (though I admit it never occurred to me) that not all communities are the same in terms of theological belief/adherence. She is able to convey the culture of one particular community from its boring Sunday meetings to its singings, from its extremely conservative gender roles to its poverty to its communal care. It's not all bad or all good; it's mostly rather normal.
The behaviors of different people within the community are also normal--the outspoken brother who will likely settle down one day and become a willing member of the community; the friend who experiments with "the world" but never honestly debates leaving; those who embrace the community's strictures; those who compromise with them (internally and externally); and those who leave.
The young men who leave both want to go (and feel it is necessary since they are in love) and don't want to go. Their uncertainty coupled with a realization that certain changes are inevitable is realistic and touching. Religion is not merely an obstacle or a thing to be overcome but an ongoing aspect of their lives; consequently, it informs the type of struggles they endure, especially in the second book when Isaac and David move to San Francisco and have trouble adjusting to "English" city life (their reactions are so thoughtfully and compassionately detailed, I suspect more research by the author).
The smartest aspect of the series, which many writers unfortunately gloss over, is the religious one. Neither member of the couple is theologically devote, but they both take God and heaven and hell seriously. Isaac's brother has gone the full agnostic route, but neither Isaac nor David are comfortable with that choice. They still pray. David--slightly more theologically minded than Isaac, who is more like his brother--ponders questions of right and wrong and what God truly wants from them. They eventually become committed, communal Unitarian church goers--one of the hardest sacrifices for them was walking away from the community of belief (despite boring services).
I maintain elsewhere that writing well about religion is hard. It helps if one treats it like an active psychological and mental and even physical factor in the characters' lives--
As opposed to a McGuffin-like obstacle to be overcome.