This is effectively settled. Every client worth using has standardized on certain extensions, and there are server capability testers for it [0].
There are still a LOT of things very much up in the air, such as message deletion, which work inconsistently from client to client, but message history is not it.
call me out if I am wrong, but isn't history dependent on the server of the chatroom creator, and doesn't every server have different history settings and does it not handle encrypted messages fully?
Yes, XMPP server implementations typically give admins full control over data retention. Different use cases demand different settings, so it's quite adaptable to whatever needs you have.
I'm not sure what you mean by not handling encrypted messages fully, it handles encrypted messages fine.
> so it's quite adaptable to whatever needs you have.
as a user you cannot, even if you self host, because you are not the one controlling message storage
> I'm not sure what you mean by not handling encrypted messages fully, it handles encrypted messages fine.
you can load encrypted messages (including keys if they are needed to decrypt them if necessary) using a fresh login such that you can read them again?
There are still a LOT of things very much up in the air, such as message deletion, which work inconsistently from client to client, but message history is not it.
[0] https://compliance.conversations.im/