Hi,
on this precarious topic, there have already been several posts here, all of which have run aground.
From a privacy point of view, you are currently completely lost if you activate pushes. If I understood the principle correctly, the data will be sent via a TLS encrypted path to the push notification gateway of rocket.chat (https://gateway.rocket.chat) and from there to Apple or Google, but the content is plain. Both rocket.chat as push gateway operator and Google or Apple have full access to your content. Please correct me if this is not true. Basically pushes are a data protection disaster. You can disable pushes in your Rocket (or use the client from F-Droid) or configure the push without content (see administration interface of your RC: push notifications/data protection). The situation would be somewhat improved if the mobile RC clients also supported E2E. I mean, that wouldn’t be the case yet. Then at least the content would no longer be readable in plain text by third parties. But with the “metadata” you will always get naked, even with E2E. This is a basic problem and not Rocket.Chat specific, e.g. also with signal, telegram, matrix. Ultimately, you have to adapt your privacy policy or deactivate pushes. Privacy statements are not worth the paper they are written on. For example, our privacy policy stipulates that data of a certain security class may not be exchanged via Rocket.Chat. Does anyone comply with this prohibition? Ping me in #ug_german channel on open.rocket.chat, then we can discuss this in detail and I can send you our privacy policy.
As an alternative you could run your own push gateway (are there instructions for this?), but then you have to build the mobile clients yourself, a lot of effort, see here. But even with your own gateway, you can only bypass the gateway of rocket.chat. You still have to push from your gateway via Google or Apple to your mobile clients. And frankly, I trust the Rocket.Chat team more than Google or Apple. 
So in the current concept it doesn’t matter to me that the data would be pushed through the Rocket.Chat gateway in advance.
In the summary: pushes are simply a terrible dilemma. This is where we really need to gather ideas to better implement data protection and confidentiality.
Some further links:
Ciao
Marcus