I wouldn't have thought of anything like that. That solved my problem! Thank you very much.

Addendum:
I have uninstalled Connman. Because I use KDE Plasma almost exclusively, I have installed plasma-nm, which accesses the network manager. Yes, that's certainly not the purist option, but it's convenient for me and it works. However, I will actually have to deal with ifupdown, wpa_supplicant and wpagui. Yes, I'm also thinking about the man interfaces ;-)

But, yes, connman apparently includes DNS caching with built-in assumption that the network world is unchanging. Not that I know much about it; for me it turned up as a debian hack when wicd was abandoned, but there may well be more history to it than that.

The easiest and best (I say) is to just use traditional network configuration with ifupdown together with wpa_supplicant and possibly its wpagui gui tool,

EDIT: start with man interfaces

I use connman. Do you think this is the Problem? Is it better to use network-manager or wicd?

you say: "That means you are not resolving anything - localhost". But why does it work with us.deb* and de.deb*?  And why do I get to other pages on the net? Aren't nameserver ::1 and nameserver 127.0.0.1 just the placeholder for the ISP's IP address assignment?

I had first run menu-config to a) enforce sudo;  b) to change hostname to localhost (from the ??default devuan);  c) to set compose key, and on earlier attempts another key as well;  d) to set locale to a certain UTF locale (prefer not to disclose);  e) to set timezone.

When trialling both images over roughly the last two days, doing $ ping deb.devuan.org repeatedly in a shell gave responses such as, "Temporary failure resolving 'deb.devuan.org'", whereas ping google.com responded ok with 0% packet loss. 

Could a significant clue be that upon attempting other cli instructions, not obviously related to networking lately (I think one was an ls instruction!) during one of those USB sessions, I have been getting the response, "Unable to resolve ... localhost.localdomain".  Is some daedalus package setting the host name wrong, such as menu-config?

As an aside (let's have a laugh!), perhaps agents (a man-in-the-middle?) may want to read diagnoses of our own systems to thwart us further during choice moments for them to intervene:  during a post-install, before a firewall is able to be downloaded?

That kills any DNS re. internet access.

This is the Google DNS server ...

For me here:

cat /etc/resolv.conf
# Generated by Connection Manager
nameserver ::1
nameserver 127.0.0.1

apt-get update
OK:1 http://us.deb.devuan.org/merged daedalus InRelease
OK:2 https://packages.mozilla.org/apt mozilla InRelease
OK:3 http://us.deb.devuan.org/merged daedalus-updates InRelease
OK:4 http://us.deb.devuan.org/merged daedalus-security InRelease
OK:5 http://us.deb.devuan.org/devuan daedalus-proposed-updates InRelease
OK:6 http://us.deb.devuan.org/merged daedalus-backports InRelease
Paketlisten werden gelesen… Fertig

There are no problems.

I replaced deb.devuan.org in the sources.list with de.deb.devuan.org and this is the result:

apt-get update
OK:1 http://de.deb.devuan.org/merged daedalus InRelease
OK:2 http://de.deb.devuan.org/merged daedalus-updates InRelease
OK:3 http://de.deb.devuan.org/merged daedalus-security InRelease
OK:4 http://de.deb.devuan.org/devuan daedalus-proposed-updates InRelease
OK:5 http://de.deb.devuan.org/merged daedalus-backports InRelease
OK:6 https://packages.mozilla.org/apt mozilla InRelease
Paketlisten werden gelesen… Fertig

No problems here either.

And I can also access http://de.deb.devuan.org/ with the browser without any problems.

tl;dr: VM had buggered up their BGP routing & I could not reach, kde.org, devuan.org or dev1galaxy.org (all HETZNER-AS hosted sites). A useful site in situations like this is https://downforeveryoneorjustme.com/. My problem was fixed only when VM fixed their routing after I emailed them.

PS BGP routing is used to traceroute to a site:

$ traceroute devuan.org
traceroute to devuan.org (116.202.138.214), 30 hops max, 60 byte packets
 1  192.168.0.1 (192.168.0.1)  1.612 ms  2.243 ms  3.152 ms
 2  * * *
 3  nott-core-2b-ae80-650.network.virginmedia.net (81.109.166.69)  22.865 ms  23.166 ms  23.401 ms
 4  * * *
 5  eislou2-ic-1-ae3-0.network.virginmedia.net (62.254.85.145)  37.897 ms  37.283 ms  43.205 ms
 6  ae21-0.lon20.core-backbone.com (80.255.9.125)  36.841 ms  15.679 ms  22.071 ms
 7  ae1-2014.nbg40.core-backbone.com (81.95.9.14)  36.162 ms  36.527 ms  37.013 ms
 8  core-backbone.hetzner.com (81.95.15.6)  35.085 ms core-backbone.hetzner.com (5.56.20.254)  36.375 ms core-backbone.hetzner.com (81.95.15.6)  34.779 ms
 9  core11.nbg1.hetzner.com (213.239.229.161)  34.982 ms  36.123 ms core12.nbg1.hetzner.com (213.239.229.165)  35.627 ms
10  ex9k1.dc1.nbg1.hetzner.com (213.239.203.226)  34.409 ms ex9k1.dc1.nbg1.hetzner.com (213.239.203.222)  33.108 ms  40.247 ms
11  bonito.devuan.org (85.10.193.185)  37.010 ms  35.436 ms  30.039 ms
12  www.devuan.org (116.202.138.214)  36.284 ms  43.089 ms  35.657 ms

2024-08-17 update: I originally said "used in ping to trace to a site" & corrected + added an example to make it clearer.

Also try host -v deb.devuan.org to get some more info.
And host deb.rr.devuan.org in case that works for some reason.

But it works for me so I can't debug it any further.

host deb.devuan.org
deb.devuan.org has address 185.38.15.84
deb.devuan.org has address 141.84.43.19
deb.devuan.org has address 147.78.194.22
deb.devuan.org has address 125.228.189.120
deb.devuan.org has address 185.178.192.43
deb.devuan.org has address 190.64.49.124
deb.devuan.org has address 67.219.104.166
deb.devuan.org has address 131.188.12.211
deb.devuan.org has address 95.216.15.86
deb.devuan.org has address 198.58.118.8
deb.devuan.org has address 195.85.215.180
deb.devuan.org has address 103.146.168.12
deb.devuan.org has address 130.225.254.116
deb.devuan.org has address 94.16.114.15
deb.devuan.org has address 185.236.240.103
deb.devuan.org has address 46.4.50.2
deb.devuan.org has address 5.161.180.234
deb.devuan.org has address 160.16.137.156
deb.devuan.org has address 106.178.112.231
deb.devuan.org has address 185.183.113.131
deb.devuan.org has address 200.236.31.1
deb.devuan.org is an alias for deb.rr.devuan.org.

ping deb.devuan.org
ping: deb.devuan.org: Temporärer Fehler bei der Namensauflösung

English: Temporary error during name resolution

Browser: http://deb.devuan.org/
Seite wurde nicht gefunden
Die Verbindung mit dem Server deb.devuan.org schlug fehl.

English: Page was not found
The connection to the server deb.devuan.org failed.

Strange and difficult for me.

You may find you can only connect to some of the round robin addresses. If so temporarily putting one of the ones that works into your sources.list should get you going (preferably one that's near to you).

Hi rolfie, how can i check if my DNS is working alright? Just a keyword, I can then continue searching myself.

Addendum: I get to devuan.org excellently and the answer is fast. But the subdomain deb.devuan.org refuses to work for me.

ping: http://deb.devuan.org: The name or the service is not known
ping: https://deb.devuan.org: The name or the service is not known
ping: deb.devuan.org: Temporary error during name resolution