Unfortunately, despite a lot of testing previous to the v25.12 release, a combination of several bugs with similar symptoms resulted in non-functional audio by default for some Qualcomm devices when specifically installing systemd and GNOME/Phosh (more specifically gnome-settings-daemon, which is a core part of the desktop).
If you are using a device with a Qualcomm chip, are in edge or stable, have a recent install of systemd with GNOME, and experience very low audio, you might be able to fix the issue by running the following command:
doas apk add postmarketos-base-ui-audio-pulseaudio
In case that does not fix your issues, you can come back to the previous status by running
doas apk del postmarketos-base-ui-audio-pulseaudio
Root causes
Some Qualcomm devices have had issues with volume under Pipewire due to audio formats for a while. There is a workaround available in postmarketOS, but it is not applied consistently to all devices. This should not have been a big deal, since in principle we are not using Pipewire's audio server by default. However, there is also an issue affecting the default choice of audio server between pipewire-pulse and pulseaudio on new installs. For some reasons that we have not yet fully understood, the combination of systemd and gnome-settings-daemon results in pipewire-pulse being installed, even when pulseaudio is expected. Progress is being tracked in !7776.
We also cannot discard further issues with Pipewire's audio server, as that is not yet extensively tested on mobile. The day we change the default, we will provide a notice and make sure that more testing is executed. Hopefully the hardware CI work can help with this in the future.
We apologize for the inconvenience this has caused, specially since this issue was overseen in the v25.12 release notes.