Thank you, @Joulinar
Restored backup, installed AdGuard Home + Unbound
Tests:
dietpi@DietPi:~$ ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether
inet 192.168.1.10/24 brd 192.168.68.255 scope global eth0
valid_lft forever preferred_lft forever
dietpi@DietPi:~$ dig @192.168.1.10 -p 5335 google.com
; <<>> DiG 9.16.37-Debian <<>> @192.168.1.10 -p 5335 google.com
; (1 server found)
;; global options: +cmd
;; connection timed out; no servers could be reached
So just as expected
dietpi@DietPi:~$ dig @127.0.0.1 -p 5335 google.com
; <<>> DiG 9.16.37-Debian <<>> @127.0.0.1 -p 5335 google.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 52924
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;google.com. IN A
;; ANSWER SECTION:
google.com. 30 IN A 142.250.185.14
;; Query time: 4 msec
;; SERVER: 127.0.0.1#5335(127.0.0.1)
;; WHEN: Wed May 24 08:51:17 CEST 2023
;; MSG SIZE rcvd: 55
dietpi@DietPi:~$
Excellent! 
Just changed DNS setting in the router and done!
@Jappe thank you to as well of course! Because I think my issue was both about the two network interfaces being enabled and the dig command. Thank you to you two.