Hey!
So, I just got the Google Pixel Buds Pro 2. For days now, the comanion app didn't show any updates for my buds, despite being clear on a very old firmware version.
A bit of research showed, that you can manually update these from you phone. In the settings app, under system updates, there should be a menu called "app updates".
In GraheneOS, the whole system update menu got replaced by the GOS team. My thesis now is, that the companion app relies on the "app update" logic in the settings app, which is (presumably) not present in GOS.
My workaround now is https://mypixelbuds.google.com/ . You can connect your Pixel Buds through a chrome browser and start the update there. This works quite well.