Maybe have just been lucky, but have never gotten those pop-ups. And although no software or device is perfect, I believe iOS is still significantly superior to Windows or Android in terms of security, both of the operating system and the software ecosystem.
For what it's worth, what we do on our Apple devices is:
1 - Keep the setting turned on to block pop-ups in Safari:
2 - Use the 1Blocker content blocker
This is an excellent ad blocker which you can download from the App Store.
Then again, maybe it helps that all the web sites I visit are fairly vanilla, and it also helps to be a dinosaur who only uses antisocial media: email, paper, etc. No Facebook or Twitter or Instagram or Pinterest or Snapchat or whatever the current fad is.
It's probably unlikely, but there's also a chance that those symptoms could result from a compromised wireless router. You can do a quick check:
Think you said you already cleared cache on Safari, but that would not hurt either.