I know. Both you and i know i have talked this subject to death. But GA4 has cracked the bounce rate ‘code’ to make it a, wait for it, useful metric. What you say- How is that possible- It is technically impossible to have a single page visit capture meaningful information like time on site.
Well, in GA4 bounce/bounce rate is really just the non-engaged user. An engaged user (session) is a session where a visitor spent less than 10 seconds (unless you changed this default in the admin), saw at least two pages or made at least one conversion. What this means is a bounce is someone who only saw one page on your site and spent less than 10 seconds (or whatever you changed this setting to be) on this page or a visit that did not convert.
The reason this is now technically possible is that there are events that are triggered for conversions (obviously) but also an automatically collected event for engagement (staying on the site for x seconds).
One other semi- related note – unlike goals in GUA, conversions can occur multiple times (and be counted/credited) for each time they occur in a session.