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.
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.