I understand many Private Trackers don't allow use of VPNs when registering/browsing. But how do they determine if a user is using a VPN? Do they do a reverse lookup on the IP address and map it to a database of known IP addresses used by VPNs? Or simply because the same IP address was used by other users (who are using the same VPN?)

If a user uses a VPN service which offers a static IP address (I understand this costs extra), would the Private Tracker still be able to identify the static IP as "belonging to a VPN"? If so, are there ary VPNs which offer a static IP which is unable to be identified as a VPN? If not, are there any other services/ways to achieve this?

The reason for me wanting to do this is just because I want to stay anonymous and safe.

VPN IPs usually come from data centers/hosting companies and not from ISPs, so this could raise a flag. You could try a proxy.

I am thinking of taking WCD interview through proxy. Is it possible to create an undetectable proxy? My country is banned from interview, do you think I can change my IP location?

It's too risky, I wouldn't do it.