In GA4 Explorations, there is only one dimension for New vs Returning Users. It's called "new / established" and the on-hover popup shows it's very clearly about whether users were new in the last 7 days or if their first visit was prior to the past 7 days.
In Looker Studio GA4 Connector, there is no "new / established" dimension. Instead there is "New / Returning", with description "New users have 0 previous sessions, and returning users have 1 or more previous sessions. This dimension returns two values: 'new' or 'returning'."
I've tested both with the same date range and while they are somewhat close, they are clearly not the same result.
Why are they different?
For our use case, the Looker Studio dimension - new or not, regardless of timeframe - is the one we need when comparing user behaviour between those who have never seen our site before vs those that have. Without this being available in GA4 Explorations, we are unable to check our Looker Studio charts are working correctly.