On my Pc , your system are put on a disk in read only…
I try to rename the lib/firmware to put a new firmware sub-directory… always say in read-only.
For audio problem…
I believe the the inability to access the lower level system directories are because of the OSTree structure. And as far as I can tell there is no way for the end user to get around this limitation. If you are having difficulty installing some needed driver software and the software has an open source license you could ask the developers to include the needed firmware/software as a direct part of the Endless OS install process.
bill
As @wove says, it’s deliberate that /usr is read-only.
In the particular case of installing additional firmware, you can place it in /var/lib/firmware: /usr/lib/firmware/updates is a symbolic link to this directory.
Thank for info…