Can you provide a source that they've said this recently? This seems to be a bit of a misrepresentation.
They say:
>The Play Store app is also the most secure way to install and update apps from the Play Store.
on /usage, but this does not indicate it's the most private way or that it's the recommended way to install apps. It seems to me to indicate that this is their assessment of the security of the ways to install apps that are distributed on the Play Store, not a recommendation or privacy assessment that applies to other apps or to their users in general.
They don't recommend against Aurora Store [1], but it is not user friendly as the Play Store because app installs frequently fail and automatic updates do not work as well. Installing apps from Aurora has the advantage of no google account, but Google is still handed a list of all the apps you have installed, IP address, app details, device details, and GSF ID. It will likely stop working or become even more broken. It is useful when apps block installs from the Play Store because of play integrity.
I use it myself for the few Google apps I install like Camera because I don't want to install play services.
I would consider their actual recommendation to be their own App Store and Accrescent (alpha).
Obtainium is great but not user friendly.
The claims about problems with F-Droid are true. It's not like they oppose FOSS, their whole operating system is FOSS and they've never said anything bad about IzzyOnDroid, which fixes the problems with F-Droid and even adds a bit of security.
[1] https://nitter.freedit.eu/GrapheneOS/search?f=tweets&q=auror...