Sometimes what should be the simplest questions are the hardest ones to find an answer to. I just want to set it so that when OPNsense goes out to get updates, etc. it uses Google's DNS rather than my ISP's, because my ISP's DNS is horribly slow. I am hoping that you do not have to make changes in Unbound, because it seems that when people do that they then have all kinds of DNS issues.
I found these settings, if I just enter the DNS I want to use in those fields will that be sufficient, or is that for some other purpose entirely?
(https://i.postimg.cc/3rm23t0c/Screen-Shot-2021-05-29-at-11-00-33-AM-show.png)
If you want to change DNS setting system wide then look under System ==> Settings ==> General, there is a section for DNS servers and option to disallow overwriting by DHCP on the WAN side.
HTH.