TheFool

If I understood you correctly ShareDrop should fix your problem, there you can "add" someone from a different network via QR-code

There is antifandom.com

Linux Distribution (Distro) and Desktop Environment (DE). Not sure why the commenter above expected you to use Linux though

Easiest seems to me just enabling E2EE in telegram since it’s there. Asking to use secret chats seems easier than asking to switch plattforms

Okay MkvToolnix isn’t the right tool for that afaik, but ffmpeg is and it sucks there isn’t a GUI for it that’s as powerful as the cli which is what I use, luckily you can find a lot of help online,

Apart from that I’m afraid i can’t help much, but good luck with your search!

Are you trying to concat streams or just to remux? For remuxing as roawre said there’s also MkvToolNix, which works great (and it has a gui don’t worry)

ffmpeg, if you need a gui use handbreak

Well that’s his signature move

Here you go

Sure you have to enable E2EE but they never say they use E2EE by default, they’re not advertising at all anyway. Saying it is "not secure at all" is a bit of a reach. They have proven they don’t share data with governments and again, you can use E2EE if you want