Thanks for reaching out. From reviewing the associated guide it looks like this new Google tag is referencing the evolution of the gtag.js method of adding a Google Tag Manager code snippet to a users site. I believe Site Kit already does support this by inserting a code snippet similar to the below on users sites: https://www.googletagmanager.com/gtag/js?id=GA_MEASUREMENT_ID
I’ll also check this further with the team to confirm that there are no changes required with Site Kit for this. I’ll report back to you here. Please allow me some time to review this and check with the team. Thank you!