At the top of my head.
Natalie Campbell left when they moved to Canada and is now CEO of her own company.
Samantha Cohen had preplanned to leave and extended for a few months to help the couple settle in their new role.
Jason Knauf was forced on them (and is Dan Wotton friend who seems to have been feeding the media, and made the bullying claim), he went back to the Cambridges - whom he is now leaving.
Amy Pickeril, another one who was said to be staying only to help MM transition from Canada to the UK. She was already set to leave and delayed it till after Archie's birth. Which she did and said they would remain in touch with her as an advisor.
Melissa Toubatti and Katrina McKeer are hinted as the ones in the middle of the bullying scandal. What we know is that one of them went back to being a nanny and one is said to have left for gross misconduct. But I cannot be sure.
The protection officer, the Met put out a statement that the officer made plans to resign already for family matters.
A nanny was a temp. Then another unsubstantiated was said to have done something unprofessional and had to be let go (though I believe this was in ff, so not sure)