I cannot switch next audio output source throughout the audio widget. There is a screencast what I was doing for that. What do I do wrong? Only after when I stop or pause playback, audio output sources switching succesfully. But during playback this feature doesn't work.

Distributive: openSUSE Tumbleweed (KDE)

For me it's working fine, with the change of the default choice.
But I was hopping to be even a faster way to change between output sources

I have found the solution
A widget called : Audio Device Switcher
https://www.opendesktop.org/p/1195707/