Hello again! Excellent to see you settling into Sinnoh so well!
To answer your question, while it’s true that on the surface, midnight lycanroc can sometimes resemble dark-type pokémon, in truth, they have about as many similarities to members of that element as midday lycanroc. In terms of battle capabilities, midnight lycanroc’s elemental balances and lean towards defense over offense (physical attributes aside) are actually reminiscent of a rock-type, and its favored battling style (aggressive, direct assaults) diverges from a dark-type’s general preference for sneak or mob attacks. In fact, regarding the latter, midnight lycanroc actually more resembles a fighting-type like lucario than it does a dark-type.
However, off the battlefield, the comparison is apt, given the typical lycanroc’s generally aggressive and sometimes difficult-to-tame nature. For this reason, if trainers are asking you for tips on caring for a midnight lycanroc, it’s fair to advise them to take care of theirs the same way you would a dark-type. (The only difference, really, is that lycanroc should be allowed to self-groom, due to their rock element—that is, only give them baths if absolutely necessary.) If, however, trainers are asking you for tips on raising a battle-ready lycanroc, it’s important to remind them that it is a rock-type and should be raised as such.