The first step would be to determine which, if any, installation use case(s) need attention.

You don't mention whether(/that?) you also re-created the block device (major:minor = 254:5) as /dev/dm-5?

I believe the next attempt would be to: a) deactivate that volume group, then b) manually remove spurious links for that volume group in /dev and /dev/mapper, and then c) activate it again.

That's on the assumption that the disk itself doesn't happen to contain some old LVM meta-data on the partitions. As you know, LVM writes stuff onto the partitions, and some of its admin scripts gets confused if there are even accidental remnants of old meta-data.

One step to deal with that would be to delete the physical volume from the volume group, then clear it fully, and then add it again.

The short answer would be that "experimental is not merged".

You may note that the sources.list point says /devuan experimental while there is no experimental section in /merged.

You may well add a sources.list point for Debian's experimental section but obviously you take full responsibility for whatever package mix you make from that. With the appropriate pinning it should be "safe".

You can usually determine which virtual terminal Xorg is using by:

$  pgrep -a Xorg

and if that says, say, vt07 you may shift to that with ctrl-alt-f7.
Or, if you have a command line, the root command

# chvt 7

will do the same.

Further, there is normally a /dev/ttyN set up for every virtual terminal N. Thus, you may use

$ ls /dev/tty[0-9]* | wc -l

to see how many virtual terminals are available.
I think that is a compilation setting for the kernel.

See e.g. man openvt and friends, and man Xorg (look for "terminal").

Maybe you mean:

# iwlist wlan0 scanning | grep -B1 ESSID

mmm I don't much care about GUI, but I don't think I would see much value in using a platform that wants to be in control how my stuff looks. Probably best for me that I keep staying away from it

@nahkhiirmees: you might rather want to use the reject statement in the client host's /etc/dhcp/dhclient.conf. See man dhclient.conf for details.

Thank you for noticing. Yes, they are all perfect again

Afaik, when you installed lvm2 it should have added itself to initrd. Though my conjecture from your other notes is that you have the lvm2 software installed some other way. Perhaps a package reinstallation would be an option?

@Grumpy, with all respect, it's kind of like contacting your bike manufacturer when you, on your way to the shop, find that there is a temporary road closure.

More precisely, the Temporary failure in resolving 'deb.devuan.org' notice is from the initial phase in the networking when the apt software (on your computer) attempts to find an IP address for that service. The service itself is not involved in that phase.