Your first paragraph is just Amazon today. They don't need AI for people to make up products and send you garbage. They probably will use AI for reviews, but they already have fake reviews that reliably fool people, so this isn't much different. If it gets so bad that Amazon's bottom line is threatened, they'll actually crack down; they're assholes, not business-suicidal.
"The entire internet will just be a computer that guesses what you want and shows you its best guess as the truth" - you just described Google Search, like, 5 years ago.
"the next 100 years is going to be unimaginable.." - not really. What we're capable of is not what happens. We only reach the minimum viable capability that meets a societal expectation. Once the expectation is reached, progress stagnates, until something exceptional changes the expectation. As a more specific example, regardless of how advanced hardware gets, software remains a gas that fills any container, so what we can actually do with the hardware is always limited by our horrible software.
People keep talking about AI like it's going to transform everything. It's actually more like colorized talking movies vs the black-and-white silent ones. Reshapes industries and changes expectations and experiences? For sure. But the films, plots, characters, actors, industry, viewers, their effect on society, etc remain the same. 3D didn't take hold, neither did smell-o-vision, drive-ins, and countless other "innovations", even though they were feasible. This is just one example, there are tens of thousands of other examples I could give. It's like a law of nature. We don't accomplish what we aren't motivated to.
Also, mcdonalds drive thrus work all the time, not just most of the time. The drive thru is the engine that generates most of the revenue; it's a conveyor belt for cash. A franchise would go out of business if the drive thru broke.