[noggin]

I see there is a new, cheaper, Google Chromecast with Google TV dongle based on the S805x2 chipset

Yes and it has Android 12 with framerate matching.. very keen to understand if this works with Kodi.

I think we worked through this didn't we?  The frame rate matching in Android 12 was support for the HDMI 'no picture disturbance on frame rate change' feature wasn't it?  The Android TV API already supports frame rate switching - though not all platforms support it (such as the original Google Chromecast with Google TV) and few apps do (Kodi a notable exception)?

Or am I misremembering?

No sane platform will offer OS-level fully automatic frame rate matching (Roku had to disable it for some apps like Netflix when they implemented it), but instead will offer something like the tvOS system of app controlled frame rate matching with OS support to enable or disable the feature. (The issue is autoplay trailers causing repeated re-syncs as you switch between 23.976, 25 and 29.97 trailers)