I am a Wire user. I am not happy that, if their server goes down, all the text and images that I shared with other users will become unavailable to me. As a special case, I am not able to look at my own old messages while using my laptop on the airplane, as the Linux client is just a webview. On the phone, it works.

Backups half-way solve the issue with text messages - I would still need to contact someone with sufficient development skills to decrypt the backup and extract the text in a readable form, but the information is there.

But with images, there is no recovery. And they apparently already lost some of my photos (the placeholder for some of them never gets replaced with the actual photo when I scroll up to year 2023).

Add to that the incompatible backup formats between the desktop and mobile apps.

So this is definitely not the claimed data sovereignty.