When I try to access IPv6-only sites, I get
user error (openTCPConnection: host lookup failure for "foo.bar")
See also #59 for an attempt at this
If you only use Linux (BSD probably works, too), you may use the patch from that pull request. For me, it's been working fine so far.
@dermesser and @melted's work is now on main and released as 4000.2.17.