This topic always warrants a good back and forth about genetics so lets start one.
Objectively speaking one generation of even first degree inbreeding is a lot less risky than the popular conceptiontion would have you believe. Certainly the idea of hellspawn genetic freaks is farcicle short of bad luck and repeated inbreeding.
What you might get is either a slight reduction of certain traits while other traits would probably be expressed more strongly. It's hard to make generalisations. I suspect that even the the risks associated with inbreeding from deleterious recessive genes matching are less important than other factors like reductions in the genetic capability to adapt to novel challenges. Though Inbreeding is practically the only way to expose and purge deleterious recessive disorders from a population.
Tthere is plenty of evidence that genetic similarity is helpful for compatibility and complex system feedback even an observed increase in fertility between related partners of around 3rd cousin.
Compounding is where it gets mirky.
edit:
I of course refer you to the work of Professor Kyuukei for further questions.
https://mangadex.org/chapter/475d1d5a-c9c9-4d6f-899f-1fb48da97b28