re: asking for help with pokemon arceus
@Felthry Cherubi and Cherrim rarely pop out of shaking trees in a few specific areas -- https://www.eurogamer.net/articles/pokemon-legends-arceus-request-17-to-bloom-or-not-to-bloom-8039
Obsidian Fieldlands - The Heartwood
Crimson Mirelands - Gapejaw Bog
Coronet Highlands - Lonely Spring, Fabled Spring, Primeval Grotto
Also, due to a bug (that they've said they'll patch soon), Sunshine Form Cherrim will always break out of any Ball; you have to find it in Overcast Form or as a Cherubi
re: asking for help with pokemon arceus
@Trinket thank you! should be able to get that, we've not seen anything other than burmy and combee come out of shaking trees and didn't know anything else could
-F