On that VPS I’ve also installed pihole to act as DNS for the tailnet.

What’s the upstream server for pihole? Is it also Quad9, or are you doing full recursive DNS with unbound or something?

Needless to say, Quad9 is not located in my home country.

Quad9 uses an anycast IP that can route to one of over 200 locations in 90 different nations, usually this routes to your closest location.

You can use on.quad9.net to check if you are using Quad9.

The Prime Minister of Japan isn’t a President, so it shouldn’t be red if we’re being pedantic.