Adguard Home installed on TrueNas Core as plugin and the webui works. The IPs provided in the setup guide does not allow me to connect when using it as the DNS.
Are there additional settings I need to be aware of?
Forget Plugins, create a standard jail with VNET and without NAT, perform
pkg install adguardhome
sysrc adguardhome_enable=YES
service adguardhome start
inside that jail.
Your jail is not configured correctly. It needs an IP address and netmask matching your network, default gateway, and DNS server. The default for DNS server is to use the same as the NAS host. So I suggest to check network setup of the host first.