One page per person you manage, and a log of dated observations that feed it. Duplicate this page and both databases come with it, sample entries included; what each one is for is in its description.
The write-up at roland.leth.ro/guides/managing-your-team-in-notion explains what each piece is for and where this setup stops keeping up. I also make Continuum, a Mac app that runs the same practice and keeps the dates checked on its own: reads keep every earlier version, tagged notes fade unless you see the same thing again, and it opens on the people you've gone quiet on. Nothing leaves your Mac, and it never scores anyone.