I have a site that has "99.9% URLs with a good page experience" (on mobile) and no issues with core web vitals, mobile usability, security, or HTTPS (all URLs pass on all fronts). This has been the state of the site for over two months now.
My understanding is that this should imply that (almost) all mobile search impressions for the site should be marked as having a "good page experience", so "good page experience" mobile search impressions should be (close to) 100% of mobile search impressions, and "good page experience" mobile search clicks should be (close to) 100% of mobile search clicks.
However, "good page experience" mobile search impressions are a little under 50% of mobile search impressions, with the percentage staying around 50% each day. "Good page experience" mobile search clicks are a little under 90% of mobile search clicks (this pattern holds for data restricted to a recent week, well after everything turned green in search console). I'm accessing "good page experience" by using the Search Appearance drilldown available in Google Search Console.
I tried digging into this by downloading CSVs for impressions broken down by page, and then diffing the CSV for overall mobile search impressions with the CSV for "good page experience" mobile search impressions. I found that in many cases, a single page has some "good page experience" mobile search impressions, but not all the mobile search impressions for that page have good page experience. Since the pages in question have had "good page experience" for the whole duration, I would expect to see all their mobile search impressions as having good page experience.