sync does not change enabled services.
IPv6 is known to cause issues with layman systems - that should be understand as one or more systems run by a user with no extensive knowledge on IPv6.
ipp everywhere is not depending on avahi but it is a protocol which presumably should be understood by the majority of printers.
avahi is network service discovery daemon which uses broadcast to the network’s broadcast address to discover services - including printers.
Since your issue is specifically targeting avahi daemon and though not strictly related - please see this comment on another topic
→ Access SLOW ".local" - Avahi mDNS - #3 by linux-aarhus