I recommend Syncthing instead of cloud services. You never really notice how much stuff is "in the cloud" but storing it all and relying on it all there is taking a big leap in trust for the service you use.
Alternatively, self-hosted NextCloud/related service might also work but involves a bit more setup. Pros of that is that there isn't duplication of files stored on mutiple devices; ie. it works more like you would expect
I'm not sure what you mean by "long-term oriented causes", but a good choice might be longtime distributions like Debian, since any good distro will spend a lot of time packaging and patching applications to play nice together. After all, one of the drivers of adoption is just making initial use of the operating system as easy as possible.
You could also investigate organizations like GNOME or KDE that also put a lot of work into developing user-friendly programs and toolkits.
Although Matrix might have a few kinks in it, I still think it’s the best choice for privacy-concious messaging. They seem to be coming up with good ideas; bridging for one is kind of functional, and I like the concept of federated systems. There also seems to be a good community around it, with lots of good libre clients in particular popping up.
I remember this organization that tries to get laptops into the hands of kids and I think that the laptops have Sugar on them, although I'm not sure. Could look into that.