How long are private chat messages kept on device or elsewhere?

I promise I have tried to search for the answer to this. I can't find a clear answer. There are a few different kinds of chat in Zoom, and a few different settings that control retention. So to be as specific as I can:

On my computer in Zoom I have been chatting with people for years. Private encrypted chat. Not a group chat. Not a channel. Not chat in a meeting. Not private chat in a meeting. Advanced chat encryption is enabled at the account level for all users.

In several of these chats I can scroll back approximately 10 months ago. Where is this 10 month retention period defined? Can I change this at the account level? (for all my users)

Is this chat history stored only on the device? If so how come I can see it on another device? For example on my smartphone I can see the history of these chats that happened on my computer.

thanks