The long-time metric of Bounce Rate in Universal Analytics will not be carried over to Google Analytics 4 (GA4). Bounce Rate is defined as the percentage of single-page sessions in which there was no interaction with the page. A bounced session has a session duration of 0 seconds.
In GA4 Bounce Rate is no more! The metric that will be used in its place is “Engaged Sessions”. Engaged Sessions are the number of sessions that lasted longer than 10 seconds, or had a Conversion Event, or had 2 or more page views. Any one of those interactions / events will allow you to understand how many users are interacting with your content on your website.
Although the new metric may have additional parameters, it is very similar to Bounce Rate. We know that a session that lasted 0 seconds or that only had 1 pageview (Bounce Rate parameters) will not be counted as an Engaged Session. You do need to be mindful with how you mark your Conversion Events. For Example, if you mark a non-specific pageview as a Conversion Event in GA4 this could artificially increase the number of Engaged Sessions which in-turn would also increase your Engaged Sessions per User.