I'm not quite clear what you're doing. I migrated my Nest account to a Google account a couple of years ago. I now logon to the Google Nest app with my Google account credentials, and I log onto the Google Home app with those same credentials. I can see our older cameras in the Google Home app, but still have to use the Google Nest app to administer the cameras and get notifications. I did not have to "add" our older cameras to the Google Home app.
Thank you for your feedback on this issue, I fully understand the frustrations of not having your new Nest Cams in the Nest App or available on https://bit.ly/3HtBgJC web app. I can imagine having to use two different apps at the moment is quite daunting, and could lead to frustration.
However, the new Nest cameras and doorbell are exclusive to the Home app because we wanted to create an integrated experience with your speakers and displays. A Nest Aware subscription applies to all of your cameras, speakers, and displays in the same home structure. Thank you for your continued patience, and support.