Thank you @Atemu !
It seems that the permissions might be wrong on the Applications or nix folder, as I get an error such as Permission Denied which looks similar to the one you link from your script : Mac Application launchers not symlinked on darwin · Issue #1341 · nix-community/home-manager · GitHub
[1] morganwattiez@Morgans-MBP> home-manager switch
warning: Nix search path entry '/nix/var/nix/profiles/per-user/root/channels' does not exist, ignoring
warning: Nix search path entry '/nix/var/nix/profiles/per-user/root/channels' does not exist, ignoring
/nix/store/bmpixa5m5fn1f9cz919z0pqcp4k93gvh-home-manager-generation
Starting home manager activation
Activating checkFilesChanged
Activating checkLinkTargets
Activating writeBoundary
Activating copyFonts
Activating darwinApps
mkdir: cannot create directory ‘/Users/morganwattiez/Applications/Home Manager Apps’: Permission denied
I’ve tried creating the dir manually, also changing permissions (chown) using different combinations, but nothing helped. I guess that I might just accept Nix is not yet the complete tool I’m looking for installing GUI apps and I might switch to Homebrew for those ones, while using Nix for other CLI tools, unless I can solve this problem 
Thank you again, @Atemu