chromium starts pulseaudio server when playing youtube for example, even though pulseaudio use flag is disabled: # equery u =www-client/chromium-79.0.3945.130 | grep pulse -pulseaudio
pulseaudio is available in system.
Is media-plugins/alsa-plugins[pulseaudio] installed?
Yep $ equery u media-plugins/alsa-plugins | grep pulse +pulseaudio
So I think any app that plays audio will start pulseaudio.