I've learned the location of Bounsweet, now I'm just confused about how I can interact with Bounsweet so I may catch it. The Pokédex isn't very helpful either since trees can't be directly shaken by the player like in Sword/Shield.
You can ram into the trees with Koraidon/Miraidon to get Bounsweet to fall.
Source
You can also throw a PokeBall directly at it with ZR if you target it with ZL.