not exactly what you asked for but there's a community project you can selfhost[1] that emulates the cloud on your own server

[1]https://github.com/ddvk/rmfakecloud

I use rmfakecloud even though i'm grandfathered in to the cloud. It's great.

I locked the fw on my remarkable 2 to 2.x and used ddvk hacks and it's just worked for years. I don't need any new features.