Yes. I'm just troubled by, again, a utility not having a proper man page, and secondly that proper documentation is not installed together with the utility. All sorts of other places of documentation is good (the man page would point them out). But all that is of course just one of the "wheels" that needs to be regularly reinvented and done differently, either just because it's possible or because the controlling generation doesn't bother to learn. It's a personal beweiling, basically irrelevant for the topic, so I'm not sure why I keep going with it.

Hopefully the @OP now finds it resolved.

It seems grub is one of those packages where it's stupidly hard to find documentation, with man pages that just say that "this is documented somewhere else and I'm not telling where"... it turns out that you need to have grub-legacy-doc installed, which provides the texinfo file with documentation using the info system.

Anyhow, according to that you should also use

GRUB_TIMEOUT=0

Afaict GRUB_HIDDEN_TIMEOUT is the time to wait before showing the menu, and GRUB_TIMEOUT is the time to wait (in addition) before booting to the default choice.

If you also have

GRUB_TIMEOUT_STYLE=hidden

then the menu is not actually shown, but the time logic remains the same.

According to my /etc/inittab my boot control script is called /etc/init.d/rc, and that is a link to /lib/init/rc, which is a shell script that by the looks of it has a great number of ways to avoid concurrent boot.
For example put concurrency=none on the boot command line.

I use google-chrome-stable for jitsi myself so I'm not to familiar with that interface, but that toggle it shows seems to be regarding the output and not the input?

I also don't use apparmor, so can't help you there. Not much use I'm afraid; I'm sure you checked through all the browser's own "permission settings".

Yes, the Devuan key was changed a fair while ago, and the easy way out would be

# apt-get -y install devuan-keyring

That package drops a couple of files:

/etc/apt/trusted.gpg.d
/etc/apt/trusted.gpg.d/devuan-keyring-2016-archive.gpg
/etc/apt/trusted.gpg.d/devuan-keyring-2016-cdimage.gpg
/etc/apt/trusted.gpg.d/devuan-keyring-2017-archive.gpg
/usr/share/doc/devuan-keyring/README.md.gz
/usr/share/doc/devuan-keyring/changelog.gz
/usr/share/doc/devuan-keyring/copyright
/usr/share/keyrings/devuan-archive-keyring.gpg
/usr/share/keyrings/devuan-keyring.gpg

with the first three being for apt.

You should rather use the "server" iso, which is intended for offline installation.

In fact, all the beowulf installation iso have the same basic installer, but they differ in their on-media pool. The netinstall pool is just enough to let you install from the network, and if you don't, you don't get a very useful system. For beowulf beta3, now available, the netinstall iso pool has been inflated beyond bare necessity to correspond to a debootstrap minbase package collection. That is still not really intended to be used for an offline installation, but it might be possible.

Offline installation is rather what the server iso is intended for, or the desktop iso, if you want a desktop environment but don't want to juggle the CD sized expansion isos for the server iso. Both server and desktop also allow network mirror during installation the same way as the netinstall iso, in which case of course the whole package pool is available.

You might need to recreate the "swap signature" within the changed partition, with

mkswap /dev/sda7

I can't really answer your questions, but thought to mention that I tend to use xrandr for changing brighness, eg

$ xrandr --output eDP-1 --gamma 1:0.8:0.7 --brightness 0.7

(The simultaneous gamma adjustment suits my display)

Use xrandr without arguments to work out the name(s) of your monitor(s). And of course, man xrandr for details.

With pulseaudio there's more fun, because it infuses itself onto the sound system by on the one hand adding a software module to replace the default alsa module at the low level, and it also adds a higher level replacement for the "default" audio path.

Forget about ~/.asoundrc since card 0 is the correct default card.

This means in particular that it adds an audio control level in between alsa and actual output.

So you may well need to install  pavucontrol-qt as well, as way of manipulating its controls. That GUI will then attempt to operate the alsa controls as well, with a good amount of potential for confusion.

With those control knobs, and those of qasmixer, you should hopefully be able to unmute whatever is muted and raise the volume on whatever is needed.

As an additional: if your pulseaudio sub system is not started you would start it with:

$ pulseaudio --start

Edit: spelling correction (thanks)

First, check with aplay -l which "hardware devices" there are (for sound).

Then check with aplay -L | grep -A2 default what the "default" is tied to.

Sometimes that is wrong since "alsa" on installation binds blindly its "default" to card 0. Then it might work by telling "alsa" to use another card, eg card 1. One method for that is to add a ~/.asoundrc file with three lines:

defaults.ctl.card 1
defaults.pcm.card 1
defaults.timer.card 1

If you haven't done so, you might also want to install qasmixer for a bit of visual view and control of sound. It might be a help if it's a question of low volumes or muted controls.

Don't cp or dd work?

I.e. just copy the iso file to the device /dev/mmcblk0 or /dev/sdc or whatever it comes up as (tail /var/log/sys usually tells that)

Is that a QA or HR question?

The support team sends their Thanks for the intended heads-up (even though they managed to get their shit together on their own this time).