You seem to have a misunderstanding of most of the process.
First of all, MCPE is only one port of the Bedrock software. It’s identical to Win10, Xbox, and I think Switch.
Second, the server platform doesn’t have to be related to the client platform. It’s just a bunch of packets sent over the internet; device, architecture, even language can be whatever you want. There’s vanilla PC edition servers in C#, Rust, etc.
Third, there is no official server software for the Bedrock platform. Any implementations would be from scratch, like Glowstone is for Bukkit.
But yes, it’d be a completely different API to maintain, because Bedrock has a very different structure.