You can see the PKGBUILD from Arch Linux (as Manjaro inherits it from there) and has nothing to change the permissions on that sddm folder
The issue was mentioned on the forum a couple of times already and other platforms/forums too:
https://www.reddit.com/r/archlinux/comments/j80skf/sddm_error_configuration_file/
https://unix.stackexchange.com/questions/555936/configuration-file-var-lib-sddm-config-sddm-greeterrc-not-writable-is-displa
And the issue was addressed upstream quite some time ago already.