I want to suggest a new step

I would like to see topgrade update the pkgfile database, if present on an arch linux system.

Which tool is this about? Where is its repository?

Its repo is located at https://github.com/falconindy/pkgfile

Which operating systems are supported by this tool?

Arch Linux, and probably anything else that uses pacman

What should Topgrade do to figure out if the tool needs to be invoked?

Check of /usr/bin/pkgfile exists and is executable

Which exact commands should Topgrade run?

pkgfile --update (as root)