You can also just sync your files. Koreader, by default, stores metadata in the same folder as the epub file. If you sync the directory with something like Syncthing, then you don’t need a server.

If you go into KDE’s settings > Sound section, what devices does it show, and what type of output (like “Digital Stereo” or “Pro Audio”) are they set to?

Once in a blue moon, my audio output will get mysteriously changed to a format that does nothing, or the audio controller will go *poof* and I need to manually re-enable it. It’s rare, and I’ve never been able to pin down the exact cause, but it seems more likely after I’ve been connecting and disconnecting alternative audio devices, like my PS4 game controller (which also reads as an audio device due to its headset port), USB microphone (same deal), or USB headphone amp.

After all these years it’s still a pain point.