London-born Alwyn gained recognition after starring in war drama Billy Lynn’s Long Halftime Walk in 2016.
Speaking to The Guardian about his relationship with the Grammy winner, Alwyn said: “It’s just not for other people.
“I don’t know how best to talk about it. I mean, I’m aware of people’s… of that size of interest, and that world existing.
“It’s just not something I particularly care about, or have much interest in feeding, I guess, because the more it’s fed, the more you are opening a gate for intrusion.”
He went on: “I think that’s just my response to a culture that has this increasing expectation that everything is going to be given.
“If you don’t post about the way you make your coffee in the morning, or if you don’t let someone take a picture when you walk out of your front door, is that being private? I don’t know if it is.
“So I just don’t really feed that.
“There are more interesting things to talk about and I just think it feeds into a weird part of the culture that I’m not really interested in being a part of.”
Alwyn worked with Swift, 32, on her eighth studio album Folklore, writing under the pseudonym William Bowery.
The collaborative work resulted in the album of the year Grammy in 2021, which Alwyn described as “a ridiculous bonus”.
Alwyn, 31, who stars as Nick in the upcoming BBC adaptation of Sally Rooney’s Conversations With Friends, also co-wrote a number of songs on Swift’s follow-up album Evermore.
He said the opportunity to work with Swift “was a surreal bonus of lockdown”.
Speaking about the experience, Alwyn added: “It wasn’t like, ‘It’s five o’clock, it’s time to try and write a song together’.
“It came about from messing around on a piano, and singing badly, then being overheard, and being, like, ‘Let’s see what happens if we get to the end of it together’.
“I mean fun is such a stupid word, but it was a lot of fun.
“And it was never a work thing, or a ‘Let’s try and do this because we’re going to put this out’ thing.
“It was just like baking sourdough in lockdown.”