@LCM
I'm just guessing at where you are really at, and don't know what cameras or doorbells you have.
If you have the older 1st gen Nest Aware subscription--which is a per-camera subscription--you can't add other cameras, but you can add additional 1st gen subscriptions for the older Nest Cam Indoor, Nest Cam Outdoor, or Nest Cam IQ Indoor if you're on a Nest account that hasn't been migrated to a Google Account.
If you have the newer Nest Aware or Nest Aware Plus subscription, that subscription covers all your cameras and doorbells automatically if they're in the same Google Nest "home" or "structure".
Regardless of the type of Nest Aware subscription, history for the newer Google Nest cameras and doorbells released starting in the fall of 2021 can be viewed ONLY in the Google Home app, while history for older cameras and doorbells can be viewed in the Google Nest app or on the home.nest.com website.
(I'm just another customer.)
Here are a couple of Google Nest Help links:
https://support.google.com/googlenest/answer/9546397?hl=en&co=GENIE.Platform%3DAndroid
https://support.google.com/googlenest/answer/9233159#zippy=
