Purely linguistic question here. What is the word for having a sexual fantasy about someone? Since this must happen a lot, I'm wondering if all languages have a single (transitive?) verb for it. If not, then why not?
Metaphor is also common in this area where direct description many be impolite. A person can be smitten or enchanted by someone. Or they can carry a candle.
I find it difficult to believe that we don't have a good word for what 99+% of people are doing since puberty and allows also to express the object of the fantasy using a simple subject+verb+object type of sentence.
Same with words for copulation (highly restricted) and even for wooing / courting, which are also pretty universal activities since times immemorial.
My response to your finding it difficult to believe is: you're asking for a word for an intensely private act! Think about how rarely people overtly and bluntly say they are sexually fantasizing about someone. When it's actually admitted to, it's done using a variety of metaphors, slang and indirect hints.
And in general, we don't have a commonly used prefix or second compounded word to turn a physical act into a fantasy. Even though "fuck" predates Early Modern there was nothing commonly attached to it to make it mental.
If you really want a single verb, "lust."
For sexual fantasies about somebody one's looking at, "undressing with one's eyes."
Auto-tagging/making clickable certain proper nouns like Homelander could be neat if there’s a way to detect them.
Lots of modern variations abound. "squished [on]" when more romantically/asexually. Couples (usually strictly monogamous) may allow each other a "hall pass", which is a noun for someone that is an (often unattainable) sexual fantasy. ("He is my hall pass.")
I think languages in general pick up a lot of nuanced terms for these kinds of things, far more than just a single transitive verb. Especially because things like sexual interest are often "forbidden" from discussion in "polite society", so a lot of it starts as euphemisms or analogies and maybe never leaves. "Hall pass" is a euphemism from childhood school days that seems to have stuck for a very specific niche.
You can find a lot of variation in places like Urban Dictionary. It can be fun to try to find old slang dictionaries from previous eras to see how much things have shifted over time. (Euphemisms tend to, especially as jobs or technologies shift out from whatever is being euphemized.)