Just as possible solution for that or another Plasma bug cases:
The problem may be caused by old cache. Sometimes, after an upgrade, the old cache might introduce strange, hard to debug behaviour such as unkillable shells, hangs when changing various settings, Ark being unable to extract archives or Amarok not recognizing any of your music. This solution can also resolve problems with KDE and Qt applications looking bad after an update.
Already tried those troubleshooting steps. No difference. 
Same issue on Intel GPU laptop and Nvidia GPU desktop.
What other issues are you getting?
The same as you described in your original post a month ago.
Th notification/progress will “hang” when using the context menu to compress a new 7z archive (or it will “unexpectedly” crash.) If you leave it long enough, and then press “Stop”, it will claim to have “failed”, but luckily your archive file is fine.
Basically, we went full circle, and with KDE Plasma 5.23.3 + Ark / Dolphin 21.08.3, using the context menu to create a new archive is a shot in the dark, with an erroneous progress bar / crash message.
Look in the bug report (submitted August 8, 2021), with the latest comment a few days ago from the lead KDE developer. It’s not very clear from whence this regression originated.
Yes. The bug is still there.
Another report has been submitted: 446006 – Ark crashed the plasmashell process while archiving (or ending archiving) a folder into 7z default profile format
But:
-) on outdated ark version only 21.08.3: I’m on unstable, but Arch’s stable still did not get the 21.11.80 version to request the update from (Arch Linux - Package Search);
-) with no debugging symbols also: Debug symbols on Manjaro - #5 by philm .
tl;dr, My entire desktop crashes and I only have the mouse pointer on a black background. The only remedy is R E I S U B 
Related to dolphin/ark … or? …
Is it says like that in journalctl? 
Perhaps it is only plasmashell process crashes but for some reason do not resurrect.
You can switch to virtual terminal ttyN (Ctrl+Alt+N), where N is a single digit.
If you have keyboard shortcut to terminal window you can start plasmashell process there and you will see desktop icon, panels again.
Yes sure, compression started from the context menu.
21.11.80 is available in KDE-unstable repos.
If you need get it , you can edit the file /etc/pacman.conf to add:
[kde-unstable]
Include = /etc/pacman.d/mirrorlist
Then update.
Seems to be the next ark version will be the 21.11.80.
I re-made the same report for the future ark version of 22.03.70 (it is currently non-released latest git version): 446049 – Ark crashed the plasmashell process while archiving (or ending archiving) a folder into 7zip default profile format
But the same problem of
persists.
I also asked KDE staff about such crash report backtraces usefulness in that fresh report.
Thanks!
EDIT
Krusader (Advanced twin panel file manager for KDE (GIT version)) got commit of
If to proceed to read it’s description:
Important note: after this patch I’ve spotted crash, same as in the bug
443540 – Dolphin crashes after packing directory to 7z.
Looks like this crash has been fixed in the KF5 5.89(git).
Depending of author’s opinion, current (git version) of KDE Frameworks fixes the crash of Krusader and Dolphin.
Manjaro’s versons are: Packages (currently 5.88 in all branches)
and
Schedules/Frameworks - KDE Community Wiki (and new version will go into Arch branches first before Manjaro unstable will get it).
NEWS
unstable branch got 21.08.3 → 21.12.0 KDE updates, including:
To upgrade (42):
...
ark 21.12.0-1 (21.08.3-1) extra 1.5 MB
...
dolphin 21.12.0-1 (21.08.3-1) extra 4.3 MB
dolphin-plugins 21.12.0-1 (21.08.3-1) extra 408.4 kB
...
but the first try to add a 20 MB folder on desktop into 7z archive via context menu still leads to:
Dec 10 21:20:15 systemd-coredump[1774]: [🡕] Process 1048 (plasmashell) of user 1000 dumped core.
UPDATE
Yesterday I got the update of
To upgrade (78):
...
kwindowsystem 5.89.0-1 (5.88.0-1) extra 802.1 kB
...
plasma-framework 5.89.0-1 (5.88.0-1) extra 4.2 MB
...
And if to try to archive a desktop folder into 7zip with context menu then
Dec 15 03:44:14 pc systemd-coredump[1736]: [🡕] Process 926 (plasmashell) of user 1000 dumped core.
(the issue remains)
7z compression was fixed in the testing branch, no error appears. 
Just four months and already fixed?
This is normal because of Open Source, KDE developers have their own freedom to improve KDE apps, no strict work. Unlike Apple company that paid developers very well to work very hard and fast.