Check if you have qt5-imageformats package installed. It is an optional dependency for kio-extras package that is not installed by default on Arch distros.

I am pretty sure webp works with the wallpaper picker on plasma5 from my experience.

You may want to play around with alsamixer. Some audio cards have really low volume on some of the mixers like PCM out of the box on Linux.

For a lot of people, louder audio subjectively means better sounding audio. (Loudness wars for audio mastering for example.)

Try installing kwallet-pam. It will remember your secrets through PAM when you log in. Arch does not have kwallet-pam installed by default unless you install via plasma-meta package.

If you use Chromium, you will not be asked for creating a password store as well so that is another bonus for kwallet-pam.

Arch and RHEL enable zswap by default. Regular x86_64 Ubuntu and Debian do not have zswap nor zram enabled by default.