CAVEAT

If you connect to a corporate VPN it doesn’t resolve the corporate internal domains!

It seems you need something like splitDNS but haven’t managed to configure it.

Main article

Currently Ubuntu does not offer an easy way to set up a “global” DNS for all network connections: whenever you connect to a new WiFi network, if you don’t want to use the DNS server provided by the WiFi, you are forced to go to the network settings and manually set your preferred DNS server.

https://andrea.corbellini.name/2020/04/28/ubuntu-global-dns/

DNS Providers:

https://securitytrails.com/blog/dns-servers-privacy-security

Chosen Provider – Quad9:

https://www.quad9.net/service/service-addresses-and-features/

Has IPV6 too.

To use or not to use DNSSEC right now

https://dnsinstitute.com/documentation/dnssec-guide/ch06s06.html