Tracking Complete Registrations in Google Analytics (via GTM)

Hi,

Is there some sort of click listener or event that can be passed in the front end that can be picked up by Google Tag Manager when a user completes their registration (after successfully submitting their username)?

Can we apply an event to the complete registration toast? If so, what is the best way to do this?

Is there another way that we can track complete registrations in Google Analytics?

Thanks!