For my Nest Doorbell Battery, I figured out how to get a reliable, loud doorbell ring set up on my phone. This wasn't an option directly in the Home app, but via my Samsung phone's main Settings.
I was able to choose from tons of notification audio files already natively or app-downloaded in my phone, but I wanted a perfect doorbell sound. So, I browsed free sound files online and found a pleasant-but-loud doorbell mp3 online and downloaded that. (I think I had to use an editor to make the file extra loud and, after I downloaded on phone, I had to move the file from "music" to "notifications," or similar file).
Then, I went to my phone's main Settings; Notifications; Home app; Notification Categories; then long press to open Doorbell Press Notifications (looks like just an on/off switch, but turn it on, then long press the words to reveal the robust menu of options).
I never want to miss the rare ring. So, in this menu, I chose: Show Notifications; Alert; Show as Pop-Up; selected my new sound from the long list of notification sound options; added Vibrate; App Icon Badge; show on Lock Screen; and Ignore Do Not Disturb.
There is a similar menu of notification options, via that path, for the Camera notifications, as well.
Interestingly, Home has just added the capability of having a doorbell ring start a Routine. I'm sure you could create a Routine to help notify you. Personally, I thought it odd and frustrating they added this, but not camera-as-trigger options.
