I like the fediverse based alternatives. Lemmy, piefed, MBin(or something like that - never tried it). Feels more like building a community. Most corparate Digital Media for me feel more like being forced to go there.

I am a linux beginner: Why obviously?

You can create a link to the Profile and mention them in the content, like this: @linmob@linuxmobile.social

If you can, wait for the new jolla phone

Signal is alright IMO.

There is no perfect service. Thats why smarter people than me analyze this and talk about it: https://www.messenger-matrix.de/messenger-matrix-en.html

I think deltachat is pretty cool. Decentralised, open source and quite easy to use and setup.For me it is something for friends willing to try out new stuff and as a fallback when signal fails.