In the case of 4chan, probably not easy to block everyone. They are on CloudFlare, so ISP's will mostly be limited to overriding DNS. The DNS servers on your ISP belong to them, so unless your ISP are doing something outright malicious, it is really up to them what sites they wish to block and they probably know you can't vote with your wallet unless you have plenty of ISP choices. I could be incorrect, so certainly read through your agreement with the ISP.

A decent method of side-stepping ISP DNS is to run Unbound DNS on your home router or a server in your home, if you can.

An example snippet from the configuration in Unbound DNS would look like this:

    forward-zone:
      name: "."
      forward-addr: 1.1.1.1         # CloudFlare
      forward-addr: 1.0.0.1         # CloudFlare
      forward-addr: 8.8.8.8         # Google
      forward-addr: 8.8.4.4         # Google
      forward-addr: 208.67.222.222  # OpenDNS
      forward-first: no

And you can view it's status with unbound-control:

    unbound-control dump_infra | grep 1\.1\.1
    1.1.1.1 . ttl 1745 ping 0 var 71 rtt 284 rto 284 tA 0 tAAAA 0 tother 0 ednsknown 1 edns 0 delay 0 lame dnssec 0 rec 0 A 0 other 0

This method of caching can also slightly improve the privacy of the people using your network. You get the bonus of a local low latency cache, and requests are distributed among multiple destinations, slightly reducing the marketing benefits of running those public DNS servers.

You can also enable TCP and TLS for recursive servers that support DoT (DNS over TLS). I prefer this over DoH, as everything in your home can benefit from it, not just your browser. Some of the servers mentioned above listen on TCP 853 for TLS. Just google "Unbound DNS TLS" There are some examples on Calomel as well. [1]

Here is an example snippet using TLS: (not the full config)

    server:
      delay-close: 200
      do-tcp: yes
      tcp-upstream: yes
      cache-min-ttl: 300

    forward-zone:
      name: "."
      forward-ssl-upstream: yes
      forward-addr: 208.67.222.222@853
      forward-addr: 1.1.1.1@853
      forward-addr: 8.8.4.4@853
      forward-addr: 9.9.9.9@853
      forward-first: no

    unbound-control dump_infra | cut -c 1-60 | column -t
      9.9.9.9@853         .  ttl  851  ping  6    var  84    rtt  342   rto  342  tA  0  tAA
      8.8.4.4@853         .  ttl  851  ping  13   var  79    rtt  329   rto  329  tA  0  tA
      208.67.222.222@853  .  ttl  844  ping  876  var  1823  rtt  8168  rto

And here [2] are a small list of public servers that support DoT

[1] - https://calomel.org/unbound_dns.html

[2] - https://en.wikipedia.org/wiki/Public_recursive_name_server