My understanding is that law requires backdoor access [111], you cannot just shrug it off as "we are end-to-end" encrypted. You must have a backdoor or not allowed to operate in Russia.
You can maybe verify that the app doesn't currently send messages anywhere, but what if there's a way for Facebook to send a request to WhatsApp for a dump of all messages within a date range?
They are supposed to do that or they are cooperating? How does it work? The local binary uploads encryption keys? The server tells the client to disable e2e?
There are public reports[1] that they are refusing to comply with similar requests eg in the UK.
For a long time e2e was optional in the messengers, not sure when the transition happened exactly. Jurisdiction user databases with contact lists, location data and like are accessible either way.
Do they cooperate?