My grandma used to mix and preserve stuff, mainly veggies,
for the winter months. (We lived in the rural north.) One of
the ingredients was the apricot seeds. The fermentation
process must removed some bitterness. I didn't like it that
much but still ate some with my morning porridge everyday.
Another piece of memory: I used to collect and crush apricot
cores and gather the seeds to sell to collectors (mostly for
traditional Chinese medicine, I think). They were not cheap
(pricier than dried orange peels) and could be a non-trivial
income source for a kid.
It might be more than bitterness that is removed by fermentation.
Sandor Katz in Wild Fermentation says:
... Certain varieties of cassava contain high levels of
cyanide and are poisonous until they have undergone
a soaking fermentation. The fermentation process
eliminates the cyanide, rendering the cassava edible
and nutritious.