Tags on itch are specified by the developer. Not by the users or itch or curators. There is a box to search for tags in browse, that is prefilled with some tags. But that is not an exhaustive list.
You can try any tag. Your topic of interest, and dislike of visual novels is problematic, tag-wise. To be blunt, not many platformer or ego shooters with the lgbt theme out there. Tags should reflect the core of the game, and being lgbt centric is often some kind of story being told with the game, the story being more important than gameplay - and such implementations tend to be visual novel like. Even worse, if your main character is under that umbrella, but the story does not revolve around that fact, it would not even warrant a tag imho.
And the problem for positive search about lgbt is the freedom of tags. There might be more than several dozen tags that would be considered lgbt. In contrast, there is one tag on steam for that. Exactly one and one only. If someone has a counter example, I would be curious.
So while you might want to search for transgender and exclude lesbian and gay on itch, on steam you could only search for lgbtq+ and exlude ... visual novels. That you could do.
One could say, the lack of tag exclusion also comes with a much wider range of possible tags to postivly search for.
Searching for tags, positve or negative has the limitation that you would have to agree with the developer, if any tag would be appropriate for the game in question. Some games are not even tagged at all.
I find stuff with related games button and recommendation page. I believe the algorithm for that looks at more than tags.
Bottom line, while a negative filtering might sound good, I have doubts, how good it would really be. I seen games being tagged visual novels that basically are point & click adventures or business management simulation, but being made in renpy, so maybe that is why they tagged it. Or because vn is popular.