google-analtyics-add-custom-properties

• Setting deviceId as a user property via gtag('set', 'user_properties', {'deviceId': deviceId}); means it will be associated with all subsequent events, including automatic ones. This is generally the recommended way to handle persistent user-level identifiers.

The custom_map in the config call within ClientTrackingInitializer (window.gtag('config', GA_TRACKING_ID, {'custom_map': {'dimension1': 'deviceId'}})) is used to map an event parameter or user property named deviceId to a custom dimension (in this case, dimension1) in your GA4 reports. For this to effectively map a user property, the custom dimension in

GA4 should be user-scoped.

Why this setup should generally work for your goal:

When gtag('set', 'user_properties', {'deviceId': deviceId}) is called, any events fired after this (including automatic page_view events if this set happens before the config that triggers them, or subsequent page_view events on SPA navigations) will have this user property associated.

User properties are automatically sent with events to GA4.