I was reading Zoom's security whitepaper on their website and it says it can "encrypt presentation content at the application layer". Now I have a reasonable understanding of E2E encryption, but if the text or content has to be presented to the user by the OS, can the OS read the content of whatever the user is seeing since it has to render the graphics?
For example, can Google read my Signal messages via the fact Android has to render the text?
An example of asymmetric encryption would be OTR (off the record), which has been used in the past to encrypt message payloads in popular chat programs. In those cases, the chat programs are entirely unaware of OTR, or may just see it as a plugin. OTR will encrypt messages with the keys of the party members for whom the messages were intended. Implemented correctly, the servers handling the transport of the communication will never see any private keys nor would "backdoors" be feasible. A chat party member would have to be compromised to glean any discernible data. This gives the party members privacy and the server operators plausible deniability about any communications.
End to end encryption of course also assumes the chat servers have no control over the applications and can not push an update the a specific person or group of people and could not mitigate or simply back-door the implementation of E2E. So for example, if I connect to an IRC server and use OTR, the most the server could do is block me for sending words that do not look like unencrypted text of a known language. It can't hijack my application. On the other hand, cell phone applications can be updated by the carrier or authorized maintainers of the application.