How can a site determine that a VPN/Proxy is being used?

Question

VPN

I recently noticed that some sites can track if VPN/Proxy is enabled or not.
As far as I understand, sites check for the presence of an IP address in a list with VPN providers.

Although the fact that sites can use a comparison of the local time zone and the time zone of the country to which the IP refers is also not excluded.

There is a special site that detects if vpn/proxy is enabled or not - whoer.net (not ads), so why even after changing the time zone it still shows that I am under vpn? How it works?

How can you hide VPN usage from websites?
How do sites actually determine this?

Answer 1

schemes and principles are different, 80 percent can be described and attributed to the well-known
most often - headers and host names