What is a WebRTC leak?
A second public IP address offered by the browser during a peer connection, different from the address the site sees.
WebRTC
WebRTC leak test
This runs in your browser, after you click. It asks a public STUN server which addresses a peer connection is willing to share, then compares them with the IP this site already saw.
A 10.x, 192.168.x, or 100.64.x address is your own network or CGNAT, not a leak by itself. An mDNS name means the browser hid the local address. A second public address can mean a VPN is not covering WebRTC.
Not run yet.
Nothing from this test is stored. The method is the ICE candidate list, not a guess about which VPN app you installed. What a leak means. A DNS leak is a different check, and this site does not run one.
Questions
Is a 192.168 or 100.64 address a leak?
No. Those are local or CGNAT addresses. An mDNS .local name means the browser hid the local address.