$ apt-cache search xdg-desktop-portal    
xdg-desktop-portal - desktop integration portal for Flatpak and Snap
xdg-desktop-portal-dev - desktop integration portal - development files
xdg-desktop-portal-gnome - GNOME portal backend for xdg-desktop-portal
xdg-desktop-portal-gtk - GTK+/GNOME portal backend for xdg-desktop-portal
xdg-desktop-portal-kde - backend implementation for xdg-desktop-portal using Qt
xdg-desktop-portal-tests - desktop integration portal - automated tests
xdg-desktop-portal-wlr - xdg-desktop-portal backend for wlroots

...and then make sure that the relevant package for their desktop environment is reported as being "installed";  in my case, with a gtk setup:

$ apt list --installed | grep xdg-desktop-portal-gtk

WARNING: apt does not have a stable CLI interface. Use with caution in scripts.

xdg-desktop-portal-gtk/stable,now 1.14.1-1 arm64 [installed]

If it's not installed, try installing it (using doas or sudo):

$ doas apt install xdg-desktop-portal-gtk

So make sure that you have pipewire and its related packages installed in the first place, and then some scripts like the ones I wrote about, plus this kind of xdg package.  I hope this helps, although I am trying to get things right myself.  If someone has a good working audio setup, please chime in, thanks!

1. Remove pulseaudio (but keep pavucontrol, as you can launch that to help set some audio levels):

sudo apt purge pulseaudio && apt autoclean && apt autoremove

2. Make sure that pipewire, wireplumber are running:  systemd uses services for that, but the solution discussed in that post helped me:

- Either set up launcher.sh to launch automatically in Gnome with the contents as described for the 'alpine solution' (the link there leads to pipewire-launcher.sh)
Comment out (put a '#' symbol) at the start of any line containing pipewire-media-session, as that is not used currently in Devuan stable, I believe.

- Or else you could enter its contents (except for the first line: "#!/bin/sh") near the top of ~/.xinitrc if you have that file.

3.  If, after all that, you still don't have sound, for now, you could try launching wireplumber, and then your browser, media, etc, could give you sound after relaunching them.  It's my temporary solution, as I haven't found a long-term solution since reporting a similar problem:  for example, in a terminal (the terminal will close, to get it out of the way):

nohup wireplumber & exit