Gothic as a genre means that no one thing is “necessary” as long as most things are arguably or generally or vaguely there. I'm interested in Early Gothic which is very location-based, but post-Frankenstein and post-Vampyre there is going to be more material for fans of the sci-fi/fantasy Monsters and the Byronic heroes.
What I think factors in is queer readings. Some are really in the text, such as Manor by Karl Heinrich Ulrichs or Carmilla by Sheridan Le Fanu.
But when it comes to something like Sherlock Holmes...just because he wiggles in his chair after his roommate ejaculates, does not mean that they're gay! It was a different time that had different words for things and different expectations of how men can act towards each other that's socially-acceptable.
In the 2010's when homoeroticism was far less stigmatized compared to the time that The Picture of Dorian Gray was published (and so nobody was going to go to jail for writing SuperWhoLock gay fanfictions) fandom subculture still gained notoriety for finding homoerotic subtext where the writers and actors and editors of these television shows didn't put it there (or even where these creators purposely kept it out.)
Brown University sociologist Alexander Avila pinpointed this tendency partly due to the mid-20th-century Hays Code restrictions on cinema in the United States—this influenced a cinematic language that trained viewers to pick up on subtext that was back then discouraged by Hays' production Code, see The Haunting (1961) or Rope (1948)—but also due to references, themes, and the framing or acting.
What Avila did not predict or point out was the idiosyncratic desire for somebody else's sexual availability (or the performance of this desire, for someone else's performance of their desire. Holden Caufield was right, everybody is a phoney!) In those cases it won't be the work itself shaping up something homoerotic whether that's on purpose or by accident, because of the themes relatable to queer experiences or references that are recognizably queer-culture...but rather because a reader or viewer individually develops that parasocial relationship (to a fictional character, or to a real life celebrity)—and then it becomes a trend.
In those cases I think there must be something in society that causes people to find homoeroticism “where there isn't any”, and I am saying we should consider this influence on our readings before we approach 18th-century and 19th-century literature.
That's in plenty of 20th-century fandoms whether that's the 1941 essay by Rex Stout arguing that “Watson Was A Woman”, or 1960's housewives and career women who were fans of Star Trek and spoke in code about “The Premise” (this premise being that Kirk and Spock had a homoerotic relationship.)
So after we check ourselves of the 20th-century and 21st-century development of Queer Reading methods or culture, I would now return to 18th-century and 19th-century Gothic Literature.
Gothic Literature explored transgressions. Ursula Le Guin referred to The Divine Right Of Kings as a power that seemed inescapable, but the late 18th century that birthed the first gothic novel was also full of tensions surrounding the fate of the monarchy. The explosion of Gothic Novels after The French Revolution is theorized (Professor Jak Peake said so in a lecture, but I traced this idea back to the Marquis de Sade's reviews of Anne Radcliffe's novels in “Idée sur les romans”) to be a way for Europeans to come to terms with what happened: the common people violated the Divine Right of the monarchy. That was so fundamental to all society at the time and in those regions, that a culture is going to have anxiety-nightmares and post-traumatic nightmares about it, and in a culture that “nightmare” comes out as novels or paintings or fashion trends and such.
I'm getting to the homoeroticism, so stay with me.
Anyway, if the Gothic Novel explores the barely-conceivable terrors and horrors of losing the monarchy...then it's going to explore other anxieties of society. Immigration, for example; Disability, for another example...Religious conflicts, women's voting rights, the future of science and technology, and yes queerness.
Gothic literature often has racially-marked characters in it, from Heathcliff (Wuthering Heights) to Queequeg (Moby-Dick) to Meg Giry and Darius (The Phantom of the Opera) and all the Romani characters in The Hunchback of Notre-Dame. Is a racially diverse cast a necessary component?
Gothic literature often has disabled characters in it, and I'm reading up on that as a personal project right now: Tiny Tim Cratchit, Captain Ahab, Quasimodo, Archibald Craven. Is a person with disability a necessary component?
Is homoeroticism a necessary component? I think that answer will be the same as the two parallel ones above.