Hey there,
I had the Google Assistant SDK added in the past, so I could control a device, which is added to Google Home, but was sadly not compatible with HomeAssistant.
Somehow, it stopped working , which resulted in me trying to reconfigure the integration about 2 months ago, which resulted in always getting a timeout on the OAuth-authentification. I thought, maybe there is some server issue at the moment and tried it again from time to time, but it never worked. I don’t know, what could have changed back then, maybe I have installed an update for HA, but I surely did not change any configuration on a working integration 
The Google Assistant Integration on the other hand is still working fine, which means Google Home can still control my HA-Devices.
To solve the problem, I removed the credentials from both google cloud and HomeAssistant and done the whole process for the OAuth again, adding new Projekt and OAuth credentials on google cloud, adding the client ID and client key when asked by HomeAssistant, but in the end, it always results in getting a timeout for the OAuth process. Tried this multiple times, always folowed the instructions for the integration, but always getting the same result, also tried it on several occasions (after new HA Updates etc.)
HomeAssistant runs as HAOS on a Raspi 5 8GB, if that is somehow relevant