Where can I find any updates on the Web Vitals metrics?

Chrome isn't being mysterious about the metrics which are part of the Web Vitals, nor about how they are measured and changed. You can find any changes of metrics as well as per metric via their Web Vitals Changelogs.

• https://chromium.googlesource.com/chromium/src/+/master/docs/speed/metrics_changelog/fcp.md
• https://chromium.googlesource.com/chromium/src/+/master/docs/speed/metrics_changelog/fid.md
• https://chromium.googlesource.com/chromium/src/+/master/docs/speed/metrics_changelog/lcp.md
• https://chromium.googlesource.com/chromium/src/+/master/docs/speed/metrics_changelog/cls.md