Actually from the spoilers I read Navier & the shitty emperor are infertile it’s just that Navier was healed by the bed her & Heinly(sorry if I misspelled his name haven’t read this in a while) used since it had magic stones or something on it
ohh yeah, that bed with the magic stones
It was never explicitly said whether Navier or Sovieshu are fertile or infertile. That was kept vague in the story and upto the reader's understanding. They could have both been infertile or fertile. Most likely, the both had some fertility issues that could have been fixed if Sovieshu had been honest and tried to get it fixed together with Navier.
Navier isnt Infertile Piece of Shit