Start by looking through MV credits for mixers. In Miuna's case, there's one mixer consistently works with her,
akitsu, who also sings.
Searching Akitsu's YT for Miuna brings up this video:
Miuna is credited for the visuals:
This hints that Miuna's PL was heavier into the visual side of things in MV production. Scrolling through
akitsu's Twitter turns some interactions with Miyuora or Mimi, currently looking for MV comms:
A
The YT is linked on the Twitter, so all that's left is to compare a sample:
Dead ringer. As though to confirm things further, YouTube recommended me Miyuora's collab with Sai (not-Raki):