Custom welcome page is a blank slate, it can be anything.
If you want a UI or behavior similar to default community launcher (e.g. pinned apps) you can do
cp -r /usr/share/httpd/noindex/nethserver /usr/share/httpd/noindex/mylauncher
and start from there.
In default community launcher pinned apps are retrieved by some jQuery code that execute a PHP script that invokes a Cockpit API.
See:
- https://github.com/NethServer/nethserver-httpd/blob/master/default/usr/share/httpd/noindex/nethserver/index.html#L201-L202
- https://github.com/NethServer/nethserver-httpd/blob/master/default/usr/share/httpd/noindex/nethserver/res/system_apps.php#L11
- https://github.com/NethServer/nethserver-cockpit/blob/master/api/system-apps/read#L122