When it comes to clients being not fully compatible - I understand where you see a problem, but I personally never encountered it. Conversations covers Android, and Gajim is on both Windows and Linux. In my experience, they work just fine with each other, and Android+Windows+Linux covers the majority.

I do use Signal with a few people who refused to use XMPP, but I’d disagree they have good clients for every platform. Because the desktop one essentially doesn’t work without a smartphone. Registering in something like Waydroid doesn’t allow binding a desktop client because it wants to scan a QR code, and Signal-Cli just didn’t work with binding a regular client. So I am stuck using the inconvenient Signal-cli, because the only alternative I saw so far would be using it on Waydroid, which is even less convenient. Not to mention that the client itself is on Electron.