I've searched far and wide, a few times a year apart now, for a novel I read in the late 90s or early 00's that I checked out from the new release section of my library(no they purged my records from back then and I couldn't find any that fit in their collection)
Immortal humans, get to choose their appearance age they stay the same at, get reassigned a new (contrived) career every 10 years - the main character was assigned water treatment committee and engineer duties and the humans would work out plans to maintain the station they were living on.
They are also assigned new spouses every 20 years or something so they wouldn't get too bored; there was a classic throw away line about making sure one of your spouses was a nympho like his(main characters) current one.
I say contrived because at the end of the book it turns out that the computers could run everything on their own and the jobs were make-work things that required the humans to be sane through responsibility/purpose and interaction with each other etc. - yet somehow the story ends in an epilogue when the main character wakes up out of some cryogenic stasis to a station full of people speaking pidgin and uneducated clamoring around a food machine in the station hallway or something.
It was a mix of utopia and dystopia depending on perspective . One of the premises was that despite immortality new births couldn't be - infertility was part of the backstory - so humans were only surviving as long as the current ones stayed alive (and as mentioned in the last chapter waking up that turned out to be a lie)