Yes it does, however I did add the /etc/xdg/plasma-workspace/env/envars.sh file myself manually.
The manjaro-kde-settings-19.0 package is not available in the arm repositories.
All other relevant packages are available, and installed, as is the plasma integration extension through the Firefox add-on store.
This is a rpi4b 4 gig, with a 128 gig sd card, running on the Manjaro arm rpi4 edition.
Here are the screen shots:
So unless one, or more packages, are not compiled, and/or setup correctly on x86_64, I'd say something locally has to be wrong (ie. missing packages, missing firefox add-on, home directory is sandboxed, incompatible theme, conflicting settings, and/or settings files, etc.).