It is not that easy to understand what you want, to me it reads like you want something like Nextcloud - i.e. your own little cloud, where you can put all your stuff, and view it through the webbrowser or the nextcloud apps, and also keep selected parts of your stuff in sync with your devices (or automatically upload photos take with your smartphone for example).

Backup of Nextcloud (or whatever you want to use) is a seperate topic. Any incremental backup tool would apply though, so there’s much to choose from. I personally use btrbk which uses Btrfs Send+Receive to push incremental snapshots to an offsite server.

that doesn’t require I keep a full local copy of all the data

If you don’t do that, the place that you call “backup” is the only place where it is stored - that is not a Backup. A backup is an additional place where it is stored, for the case when your primary storage gets destroyed.

Ohhh yesss, I’ve been scratching a nostalgia itch recently too with turbo, tilde and mc. I’ll absolutely try these, looks awesome! Maybe some fitting hardware would be cool too, like finally getting something with risc-v, a nice clickety-clacky keyboard and an epaper screen…

One of Germany’s public broadcasting services also started running an instance for anyone part of the federal media network: https://ard.social/about

Translation:

ARD.social is a basis for ARD’s appearances in the #Fediverse network, an amalgamation of various platforms and projects. Regional and nationwide brands, broadcasts, programs and institutions of the federal media network can create profiles at ARD.social. The Mastodon instance ARD.social is operated by Norddeutscher Rundfunk (NDR).

Also the Tagesschau, which is the most important television news show in Germany, is there.