I screwed mine up recently. The above settings were set before, and I've gotten a beep since I got it. Post-screwup, I tried accessibility settings to no avail. Things that were changed beforehand (perhaps - new P7P and I've been both tinkering around and busy - plus I sometimes plug in a DAC and use Neutron Player, which is very possessive. So I can't recall when I noticed the lack of a beep precisely within a day's usage).
So, things that might have affected it:
I allowed Google Assistant to access my screen, and I enabled flash screen when it does so.
I upgraded from the December to January patch.
I upgraded, afterwards, with the small Play Store patch.
I enabled... what's it called - verbal shortcuts like "Answer" that don't require "Hey Google" first. <- Given that Google's reason for zapping the beep was to save response time, I'm suspicious of this, but I've changed quite a bit, so further testing is required.
I'll post if I get the beep back.
***What follows isn't necessary to the topic.***
It's daft that this is even an issue that can't be solved simply with a toggle. Or better, actually asking Assistant to reply when summoned with a beep or phrase, perhaps "Yes, Sir?" In an era with ChatGPT, we ought to be able to at least choose efficient or chummy. Google knows more about me than most friends, they could at least be friendly about it.
[I'm using an unlocked P7P from Google. I'm on Verizon with an eSIM. I have Assistant set so that it's constantly listening. And I've generally got things set to try out everything no matter how intrusive. Hey - it's the first phone I've actively chosen since my Note 4; I wanted to see what we've been given for all that's been taken away. I'm disappointed at all the features that ought to be helpful to my aged father, but are too difficult to use for someone intelligent that can't learn new things well. I'm also seeing just how vastly intrusive it is while saying, carefully, that it isn't. GrapheneOS may be in my future - perhaps because I simply can (goodbye forever, dedicated Verizon phones).]