SOLVED. YA? Post Apocalypse SciFi/ Fantasy. Boy escapes underground silo/ bunker city. Read around 2016-2021.

[Smithy]

Boy escapes underground silo/bunker city
Post apocalypse-scifi-fantasy/possibly YA?
Read within the last 10 years, and more likely, within the last 5 years.

Story starts in an underground city – possibly an old silo/bunker - somewhere people have gone to avoid some type of cataclysmic event, I think.
The main character is a young boy to begin with, and he has a little sister. They live in a small apartment type place with their mother. The mother (possibly a nurse?) and other mothers in charge of young children, avoid emotional relationships with their kids because they know the children will have to go to the main facility for allocation and training when they reach a certain age (about 7). The mothers usually never see the children again, so they try to maintain a distance to avoid heartbreak. I think the 'mothers' were allocated to certain men to meet a breeding type requirement.
Anyway, as decreed, the boy is escorted to the main facility by his mother at the appropriate time. The head of the silo city later turns out to be the MC’s son. During his training – where many of the children die in the process - the boy becomes close friends with another boy and girl from his group. As he gets older, the boy begins to question why they are all still in stuck in the city and starts learning and discovering what is really going on. He and his two friends eventually succeed in climbing out but the others stay behind to cover their tracks, while the boy continues to investigate the ‘outside.’ The boy eventually discovers a whole new world.
There was a multi dimension element too. I remember the main character finds a village (no technology used?) and makes friends, learns to hunt etc, but there's a baddy ‘overseer’ type element in the new world too. It takes a while for the MC to get back and get his friends out of the silo city, and then everyone else.
I can’t recall if it was a standalone or a short series.
Can anyone help?

[Mark]

Sounds very similar to This Time of Darkness by Helen Mary Hoover (1980 book but a timeless dystopian classic).

[Bargle]

Link This Time of Darkness by Helen Mary Hoover.

[Smithy]

Mark wrote: "Sounds very similar to This Time of Darkness by Helen Mary Hoover (1980 book but a timeless dystopian classic)."Not the one, unfortunately. And main character is definitely a boy. I'm not sure how it happened but after he escapes the city, he later ends up in an alternative world somehow and ends up staying up in a tree for a few days (I think this was after he escaped his first almost-run in with the overlords in the new world - from memory the scene was a bit Stargate-ish, if that helps...) while he scopes out the lay of the land before he later comes across the village...

Mark wrote: "Sounds very similar to This Time of Darkness by Helen Mary Hoover (1980 book but a timeless dystopian classic)."

Mark wrote: "Sounds very similar to This Time of Darkness by Helen Mary Hoover (1980 book but a timeless dystopian classic)."

[Smithy]

Yeah! FOUND IT! It's called "The Amber Project" by J N Chaney :)

[David]

Congratulations for finding your book.

For future reference, The Amber Project by J.N. Chaney.