My browser (Vivaldi) does not send any accept-language or similar headers for my native language.
Its user-agent does not contain my country or preferred language.
My proxy is verified at https://ifconfig.co/json to be in Netherlands and nothing about it hints at it being located in my actual country, which isn't even geographically close.
Before trying this again before asking this question, I have fully deleted all browser data.
My actual location is not USA, Germany or any other "default" location. It's a minor country.
Yet, in spite of all this, when I go to https://www.storz-bickel.com/ , the "geoip" (that's what they call it in the HTML) region auto-picker in a couple of seconds switches from nothing to my actual country.
I have gone through all the settings of the browser and removed anything such as "WebRTC" leaking my real IP address, and I have uBlock Origin to aggressively block all kinds of trackers which could possibly be telling the site some sort of historical data about my actual location.
This seriously freaks me out. How could they be figuring this out?