Question about user services, nextcloud in particular

I am setting up a nextcloud instance on nixos. That is very convenient because of the high level service config. That service is now running as the root user but I would prefer to have a systemd user (or normal user) run the process. After looking at the source nix file I found multiple mentions of a “nextcloud” user being created (like here). But when I look at the systemd service (with systemctl show -pUser phpfpm-nextcloud.service) I see that it is run as the root user.
Now I am not sure if I am just not interpreting the definition file correctly and there is no user creation or if I am doing something wrong to make the service run from a user profile.

In the nixos 23.11 branch there is this definiton at line 998 and the service is configured to run as that user in line 976.

i looked at the processes and all the sub processes run as the nextcloud user but the master process runs as root.