Lightdm-webkit2-greeter no longer accepts the password submission (due to webkit2gtk)

Yes - I read your comments.

Also the one where you prefer fixes to workarounds - Linux is all about workarounds :grin:

If you check the Packages web and search for webkit2 you will find that all related packages was updated the same day.

Another topic referring to back-in-time issue on Arch forum and eventually the Arch bugtracker

The webkit greeter was a project of Antergos and the project is not developed anymore (archived)

Comment on Arch bugtracker with reference to the webkit-greeter

Edit: I think project is abandonned, repository is readonly, I will switch to lightdm-gtk-greeter, this one works
FS#70099 : [gobject-introspection] lightdm-webkit2-greeter fails to run now since gobject-introspection update

This brings me back to my statement on theme maintenance as the greeter is depending on the Gnome theme API which has changed and is a likely cause for the greeter to fail.