Puppy holds pee and poop over 8 hours?

Hi everyone! This is already my second post here, but nothing seems to help, so I have to ask for advice again.

The problem is that my puppy simply won’t do its business outside unless we literally stand in the yard for 8 hours. The puppy is 5 months old and can easily hold it for over 8 hours. Every time we come back inside after 8–10 hours, it immediately pees a huge puddle and poops right away. So clearly, the puppy is holding in its pee and poop.

The puppy might go outside once in the morning, but won’t do any of its other business outside during the day. It doesn’t seem scared when outside—it sniffs around and explores its surroundings curiously. We’ve also rewarded the puppy a lot immediately when it does go outside, and we’ve never punished it for accidents indoors, so I really don’t understand what else could help.

Is there any other solution besides standing outside for 8+ hours every day? We’ve tried both standing still and moving around, but neither really helps.

What should I do? I’m completely exhausted from having to stand outside for 10 hours every day. Please help me in anyway I can't wait 10 hours every day, I have work.

She is a sheltie 5 months old and I have had her since she was 2 months old.