Google announced that they will begin provisioning GA4 accounts for sites who have not yet taken action, starting in March 2023. This will consist of a basic setup closely matching your existing UA account.

Provision GA4 account manually: If a GA4 account has not yet been created for you, you’ll need to create one immediately to ensure adequate historical data. UA will stop collecting data in July of 2023 for free users. For users on a paid version of Google Analytics (Google 360), collection extends out to July of 2024. Be sure you have turned on GA4 before the historical data is no longer accessible. For existing UA properties, Google has a Setup Assistant feature in Google Analytics to help with this transition.

measurementID
GA4SA