how are existing Steam prefixes detected?

[dk1953]

I'm using Flatpak versions of Bottles and Steam. I have "Steam Proton prefixes" enabled in Bottles, and the appropriate paths enabled in Flatseal. However, Bottles only detects some of the Steam games I have installed. I have a large existing library from an old Windows installation, and these were automatically detected by Steam.

For example, I have existing installation of Skyrim SE, and I ran it at least once so that its compatdata folder is created. Still doesn't appear in Bottles.

The Steam prefixes that do appear in Bottles appear to be games that I've installed directly from Linux Steam. I'm struggling to understand how and why Bottles only finds these games -- in any location that stores data about installed games, I would expect all games to be listed. Bottles' detection method doesn't seem to account for my edge(?) case.