IPv6 does not seem to be the issue here.
Likely, your fd00::10 is your Pi-hole, and I'd assume it would run in a slightly under-configured Docker container, lacking the FTLCONF_LOCAL_IPV4 recommended variable. But that would not contribute to your issue of Pi-hole being by-passed.
This reinforces that Pi-hole is being by-passed.
Some antivirus packages sport DNS features which would force DNS traffic of the machine they are installed to some alternate DNS servers.
Do you run e.g. AVG Secure DNS or AVAST Real-Site?
You'd have to disable those features in your antivirus package to have Pi-hole do its filtering.