To set up Enhanced Conversions without an email address in the datalayer, you should set the User-Provided Data variable in Google Tag Manager (GTM) to Automatic Collection. This allows the capture of any available user data in the website's code, even if the datalayer is empty upon form submission or purchase.

If Google Ads shows a notification that Enhanced Conversions 'Requires Attention', it is an indication that sometimes user data is not being sent. This notification is a prompt to check the data being sent and is not a cause for concern. It's Google's way of saying: "sometimes you're not sending me user data, please check".

Yes, it can be effective to use Enhanced Conversions with Automatic Collection in GTM. Although it's not perfect, it allows for the capture of user data that is available in the website's code, and it has been observed to work properly for many clients, even when the datalayer is empty upon form submission or purchase.