We are currently using the Universal Analytics tag (GA3). Google just released GA4!
We'd like to upgrade to the new tag because it does so much more, but I doubt Sites has that ability yet. I'm sure it could be setup as an automatic detection mechanism (the ID's are clearly different) or, probably more easily, two different fields on the analytics page.
This is different from but relates to https://tithely.canny.io/websites/p/analytics