Does Galar Mine add {*}{*} to the Retreat Cost of a Darkness Pokemon with Hiding Energy attached?
Nope, if a Pokemon's Retreat Cost is set to zero by an effect such as Hiding Energy, it cannot be increased by Galar Mine.
Source: Darkness Ablaze FAQ (2020-07-31), TPCi Rules Team (2020-08-13)

Relevant cards

Note: All applicable cards may not be listed below.
SWSH3_175
SWSH3_175