Unless you are using DoH or DoT it does not matter which DNS server you have configured on the modem/router, DNS requests are sent as plain text so your ISP can still see them and will know which sites you are seeing.
OpenWRT with DoH or DoT bypasses that problem, alternatively a VPN with custom DNS. Also a Pihole or Adguard instance never hurt. But at the end of the day someome owns those DNS servers and will likely log your use.
I just don't have the time for it or well, I do, but I don't wanna put effort into mantaining ratios and whatnot. I have stuff to do that I enjoy more than be part of a internet club.
But that's just me.