This is a follow up of this closed thread: Deepin-desktop: chromium: xdg-email: no method available for opening 'mailto:'
Basically if you run
xdg-email "firstname.lastname@example.org in Manjaro Deepin and it gives you
xdg-email: no method available for opening 'mailto:'
what you should do is edit the file
/usr/bin/xdg-email and under the line "DEEPIN|Deepin|deepin)" change the variable "DE" to "gnome".
This fixed my issue.
What I want is for other users to not have to make this manual fix.
Have a good day