Google announced that from the first of July 2023, the previous version known as Universal Analytics will no longer be processing data and GA4 will become the default option for Google Analytics tracking.
Other than the look and feel of reporting dashboard differences, you can still easily connect your google account and get data fed into Google Analytics. However, if you have been importing goals (transactions or newsletter sign ups) from Universal Analytics to Google Ads, you would need to import GA4 goals and set the Universal Analytics goals to secondary.
GA4 and GA3 measure and track data very differently.
GA3/Universal Analytics measurements are based on sessions, whereas GA4 measurements are based on events and parameters.