You can download “content blockers”, such as Adblock Plus (simpler) or AdGuard (more list options and customization), from the App Store. Then, in Settings>Safa

You can download “content blockers”, such as Adblock Plus (simpler) or AdGuard (more list options and customization), from the App Store. Then, in Settings>Safari >Content Blockers, you enable the filter list(s) provided by that app (most apps have tutorials for this). (This is similar to the way call-blocking apps work.) Notably, content-blocking apps do not have access to what is being blocked, they can only provide block lists. Also, the Shortcuts app allows you to manually run custom JavaScript on webpages in Safari.