I've asked ChatGPT how long would it take to watch every single video on YouTube...

And this is what it told me:
Short answer: on the order of thousands–tens of thousands of years.
Below I show the assumptions and the arithmetic so you can see how the estimate was made.

Assumptions

YouTube has been receiving uploads for about 20 years (≈2005–2025).

Minutes in 20 years =
20×365.25×24×60=10,519,200
20×365.25×24×60=10,519,200 minutes.

I estimate three upload-rate scenarios (hours of video uploaded per minute):

Low: 300 hours/minute

Moderate: 500 hours/minute (a commonly-quoted ballpark in past years)

High: 1,000 hours/minute

Arithmetic (step-by-step)

For each scenario:
Total hours of video ≡ (hours uploaded per minute) × (total minutes in 20 years).

Low (300 h/min):

300×10,519,200=52,596,000
300×10,519,200=52,596,000 hours →
52,596,000/(24×365.25)≈6,000
52,596,000/(24×365.25)≈6,000 years (if watched 24/7).

Moderate (500 h/min):

500×10,519,200=87,660,000
500×10,519,200=87,660,000 hours →
≈10,000
≈10,000 years (24/7).

High (1,000 h/min):

1,000×10,519,200=175,320,000
1,000×10,519,200=175,320,000 hours →
≈20,000
≈20,000 years (24/7).

If you only watch 8 hours per day instead of around-the-clock, multiply those numbers by 3:

Low ≈ 18,000 years; Moderate ≈ 30,000 years; High ≈ 60,000 years.

Important caveats

These are order-of-magnitude estimates. The real total depends on actual upload rates over time, how much gets deleted or made private, and average video lengths.

YouTube keeps adding new content constantly — even if you somehow caught up to everything uploaded up to today, new uploads while you watch mean you’d never truly finish.

The “moderate” scenario (≈10,000 years at 24/7 watching) is a reasonable headline figure to quote for a back-of-the-envelope answer.