PWA Statistics

You could listen for the appinstalled event for installations: https://web.dev/customize-install/#detect-install

For active users, you could filter the start_url parameter of the Web App Manifest to add a query parameter, for example:

add_filter( 'web_app_manifest', function ( $manifest ) {
    $manifest['start_url'] = add_query_arg( 'source', 'pwa', $manifest['start_url'] );
    return $manifest;
} );

Then for active users you could look for URLs that have ?source=pwa query parameter.

See also https://petelepage.com/blog/2020/08/measure-understand-how-installed-pwa-users-differ-from-browser-tab-users/