Some sites (eg Google) offer child friendly versions where safe search is enforced, by accessing the site using a different set of IPs. Some DNS providers (eg Cloudflare 1.1.1.3) automatically resolve to those safe IPs when available.
The government should require sites with "unsafe" content to make "safe" versions available (eg force safe mode, readonly, no signup). Sites that are wholly inappropriate for children should self-report so they can be made unresolvable by child-safe DNS.
I'm not saying this specific implementation is the one true way, there's alternatives and ways to work around it. My real point is that the government should have forced sites to implement a consistent method of enforcing child safe mode, that can be easily set in a blanket fashion by the parent.
I'm sure whatever approach will be "too technical" for many parents at first, but once a consistent safe-mode method becomes clear, I'm sure UIs and parental controls will evolve to make it easy to enable.
By default for me (in the UK) it still seems possible to view porn in a Google image search in an incognito browser tab. I don't think non technical parents can be expected to change their DNS settings to something safe to block it. I'm a bit unclear as to what the online safety bill is solving if Google can ignore it.
ISPs can provide dns or ip filtering by default which can be opted in or out in the account control page.
In fact I thought they did.