It's fair to assume with warrants Meta grants key access, but government agencies also engage in Harvest Now, Decrypt Later practices, where they collect encrypted data in order to one day decrypt it.
Discussion
my understanding is that meta doesnt have the keys...it's only at the client but am I mistaken?
Leaked Federal Bureau of Investigation Lawful Access papers
Whatsapp's information for Law Enforcement Authorities:
https://faq.whatsapp.com/444002211197967/
Rolling stone article:
I recommend checking out this website that compares different messenger apps:
https://www.securemessagingapps.com/
Generally the less information the platform is capable of having the better.