You can block sites with the in-house settings on iOS, go to:

Settings > Screen Time > Content & Privacy Restrictions > App Store, Media, Web, & Games > Web Content

You can use their "Limit Adult Websites" setting which is a great help for stopping p*rn addictions. Not perfect, but definitely useful.

If you don't want to Siri to overreach and "accidently" block the entire internet, you need to add a single period, ".", under the "Always Allow" section. This tells iOS to allow every website by default.

You then can start adding keywords for the sites you want to block under "Never Allow". iOS gives your blocked sites higher preference so even if you've allowed all websites with "." you still can't access the sites you add here.

You can look up the settings for this section, but it does lack some functionality, as you can't white list domains so that they are always allowed which I would love to do with all the login redirects google likes to use with "YouTube" in the URL. It's annoying 😡.

Sadly this is limited by what Apple allows for Third Party apps in accord with the ability to block things.

Agreed, there should be a database of sites by category (for example social, adult, business, games, etc.) and you should be able to brick sites not only the ones that are frequently visited.