Make Pi-hole work on a VPS server?

Question

Information Security

There is a VPS server in the oracle cloud. Free, so there is only one available location, in Frankwort.
"My" servers live inside a small local Virtual Cloud Network, from where they already have access to the Internet, albeit with an individual white ip. The firewall is configured for the entire network at once. Worth ubuntu.
Armed with manuals, I set up OpenVPN and Wireboard - ok, there is a blocking bypass, although the ping is unpleasantly high.
On the second server: I put Pi-hole through curl -sSL https://install.pi-hole.net | bash- the server's Internet access breaks, although it remains available via ssh.
Ok, I recreated the machine, installed pihole in docker, there is a special instruction in the manual about spec. ubuntu setup.
After opening tcp-80, tcp-53, udp-53, tcp-443 (the shortest of all that are forwarded in docker) ports, I can go to the Pi-hole admin panel.
Forcibly I specify the dns-server on the working machine - I lose access to the Internet, "dns-host not resolved".
There are requests from 127.0.0.1 in the logs, but the list of clients is empty.
To the heap, the last action I tried to install WireGuard on the same server, in an attempt to go to the Internet via VPN and immediately with filters - access to the admin panel breaks, ping also does not work, although ssh access remains.

Not at all a connoisseur of Linux and network technologies, help with sensible instructions on how to surf the Internet?
The global goal is to cut ads and (occasionally) increase security when working with unknown wifi.

Answer 1

So pi-hole itself is a DNS server, which according to filters requests to ad servers.
The official manual considers installing it on a malika on the local network, and indicating the raspberry DNS server on the router.
The problem is to do it from a virtual machine in the cloud.