I'm one of the people working on https://github.com/web-platform-dx/feature-set. Only 4 features are only marked as Baseline currently, for a minimal initial launch on MDN. The ambition is to cover the whole web platform, and at that point a list of all Baseline features could be generated.
Interop 2022 organizer here, working on Google Chrome.
By and large, prioritization was driven by web developer signals. Results from State of CSS 2021 [1] were quite influential, but we also referred back to the 2020 MDN Browser Compatibility Report [2] and the 2021 Scroll Survey Report. [3]
I think Subgrid, Viewport Units and Scrolling are clear cases of features that web developers want or struggle with, and which I'm very happy are included in Interop 2022.
This doesn't tell the whole story, though. The Web Compat focus area and "Editing, contenteditable, and execCommand" + "Pointer and Mouse Events " investigation efforts are rather motivated by site compat issues that affect users.