Btw, here's the guix home configuration file I used to add the contents of flatpak.sh into my ~/.profile, in order to update the XDG_DATA_HOME env var.
(use-modules (gnu home)
(gnu home services shells)
(guix gexp)
(gnu services))
(home-environment
(services
(list
(simple-service 'flatpak-service
home-shell-profile-service-type
(list (local-file
(string-append (getenv "HOME") "/.guix-profile/etc/profile.d/flatpak.sh")
"flatpak.sh"))))))