Great news - Your suggestions:
“pamac install python-pyqt5 python-pyqt5-sip” followed by “Uninstall manuskript, delete the ~/.config/manuskript and ~/.local/share/manuskript folders, or make a backup of them, reboot the system and reinstall it again.” seems to have done the trick (I deleted those Manuskript folders without backing them up).
After reboot, I reinstalled Manuskript and kept it open for a while with a couple of documents. No crashes or anything.
The only side effect was upon rebooting, before the login screen I was greeted with a window stating” Configuratio file “var/lib/sddm/.config/sddm-greeterrc” not writable. Please contact your system administrator.”
But I fixed it quickly with:
sudo chown -R sddm /var/lib/sddm/.config
Now everything runs fine, and all is right with the world. Thank you so much for all your time and help. You Manjaro team members are absolute diamonds. Cheers 