The apps I install from F-Droid often help me block ads in my browser, so I see very few ads as I use my phone day to day.

Meanwhile, my understanding is that Apple's App Store has ads in it, but that's the only app store allowed. So it seems like maybe iOS is the one that "has ads in the operating system".

Also as it happens I don't even see those because I exclusively use FDroid at this point. So ironically I see no ads when using a device designed and sold by an advertising company and haven't for years.