I set up Matrix a few days ago. I installed the telegram, whatsapp and signal bridges, so that I can have everything in one place. You can choose between different client apps for web, pc and mobile. Everything now works great behind on my VPN without any open ports - I could open a port and use matrix itself.
Yes. If you’re into selfhosting you should definitely give it a try. Under the hood it uses the Whatsapp web feature as far as I can tell. You’ll need the Whatsapp app on your phone or a spare one. But as I only use it for a few days, I can’t tell you more about outages - maybe when they change something in Whatsapp web.
I am not an expert, but chat control and interoperable protocols are two different things, aren’t they? With stopping chat control you wouldn’t stop the law that’s restricting signal’s e2e-problem.
Edit: As far as I can tell after searching a bit, interoperable protocols will be requiered by the DMA, but only for plattforms. So you seem to be right, that chat control will be the big jeopardy for smaller ones like signal.