I've made the test, years ago, of altering the DNS Server addresses that my computer connected to, to the ones given by the "OpenDNS Family Shield" service (https://www.opendns.com/setupguide/#familyshield) and it worked. And, I know that routers nowadays also allow you to do the same. (If yours doesn't, just buy a new one.)
However, I think that the problem here is mainly a political one...
If every government agrees that pornography is harmful to children, it should take steps to prevent easy access to it.
Like, (1) forcing every pornography website to move to a .XXX address, in order to allow an easy block of such websites, just by blocking every website with such domain name in our routers and such, or (2) making it mandatory to control access to such websites, somehow, on the ISP side, and having the client (i.e. the adult that pays the ISP) have to specifically choose the option to access pornography websites or not.
In the UK, the government is trying to control access to these websites (https://www.wired.co.uk/article/porn-bl ... d-explains). And, in Russia, the government has simply banned access to the websites that don't solve this problem themselves (https://www.bbc.com/news/technology-37373244).