So we have problems with Pixel 6a now. Google removed all the images for Pixel 6a except the last 3: July, August and September, all on Android 16: Images OTA complètes pour les appareils Nexus et Pixel | Google Play services | Google for Developers
So no way to downgrade to Android 15 to install /e/ OS with the official tools.
It looks like they did this because of battery issue (also mention in this forum here: Pixel 6a battery overheating, and Google workaround software update - #7 by mossroy ), but it also looks like their fix is making it worst: they are basically dividing the battery capacity per two, to unsure it won’t over heat. So people report that the battery capacity went from 4400mAh to 2700mAh and they are now trying to flash back to Android 15, despite the risk of bricking the phone.
You can read this XDA thread if you want to try to do it, it even contains a link to Android 15 image (which is not provided by Google anymore remember): https://xdaforums.com/t/hey-guys-i-just-rollback-to-android14-success.4750539