Problem understanding a grub.cfg line with search.fs_uuid
hd8,gpt5 is just a hint for GRUB, which is used when uuid is found more than once (multiple partitions with the same UUID).
A full version of the first line could look like:
search --set=root --fs-uuid <uuid> --hint hd8,gpt5
That hint could be, in the most cases, safely omitted (or fixed to actual values without any risk of ending up with an unbootable system).