Dogs are not people. They can't read or operate phones. They find their fun in other things. And they sleep much more than humans do.
I have two dogs and currently everyone is at home. The dogs could be doing all sorts of things, but they're doing precisely what they'd be doing if we were all out. They're fast asleep.
In normal times, they're often left for six and a half or seven hours, three days a week. They're fine with that. We built up to it slowly and sometimes I've had to nip back home and they're never pacing or whining. I know they're dead quiet, in fact, because my neighbour told me so. They get a longish walk off-lead before I go to work and another one as soon as I get home.
So I am not anti dogs being left, provided they can get outside - and they do have each other.
All that said, nine hours, even with a walker coming in, is way too long to leave a puppy or young dog. I'd be like OP, I'd be desperate to keep the puppy, especially with other parts of life going to hell in a handcart (the business...). I was lucky when mine was a puppy, there were family members around most of the time until she was seven months old. Then I was able to come home at lunchtime for an hour and take her out - but even then, we had a neighbour who loved her and almost always took her for a run mid-morning until she was about a year. I carried on with the lunchtime run home for another year. So she was two before she was left, with canine company and outdoor access, for seven hours.
OP, you really need to ask around locally and see if there's someone who'd like to have your dog part-time (my SIL did this at one stage, elderly dog-loving neighbours who didn't want a dog were thrilled to have hers a few mornings a week). The odds are good that you'll find someone.
But if you can't... Leaving a young dog as you suggest isn't fair. You might have to find him another home.