I believe plenty of other novels / mangas have gender-change as the premise in an isekai setting. Not sure how it is relevant here though.

Also, the answer to your question is probably the same as that to a rephrased version of your question, which is applicable in the real world:

So if yumiella was a guy before going through sexual transition, and he/she bangs Patrick. Is that gay or?

Why do you care? (Seriously, I can’t think of any good reason why anyone would ask this, but maybe that’s a failure of my imagination.)

Is this a hypothetical question or do you think Yumiella was actually a guy before?