Editing DNS on newer wrt build

I finally got around to flashing an MX4200 I bought last year to OpenWRT to replace my old router also running Openwrt.

Some settings have moved around and changed in newer version as have apparently some of the terms they use.

So I need to point the new router setting to use my server running Adguard and Unbound as the sole DNS server. Where do I find the new location in settings and is the process going to be the same as doing it on the old router?

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Also how to I turn off IPv6 altogether