Meta issue to track Tor v3 support. It needs:

• Finalize BIP155:
  • Get this merged: #907 BIP155: include changes from followup discussions
  • Get this merged: #967 BIP155: clarify variable integer format and change time to fixed 32 bit
  • Decide how to signal for addrv2 support - protocol version bump (as in the BIP), service bit or a new p2p message (as in the WIP implementation). Integrate that decision into the BIP (either via the above PR or separately). Done: BIP155: include changes from followup discussions bips#907 (comment)
  • Flip the BIP from Status: Draft to Status: Final
• Implement BIP155
  • Rebase pull#16748 [WIP] Add support for addrv2 (BIP155)
  • Get all unit tests to pass (pull#16748)
  • Get all functional tests to pass (if they don't) (pull#16748)
  • Address review suggestions (pull#16748)
  • Create a new PR from above (ready for review). Done: pull#19031 Implement ADDRv2 support (part of BIP155)
  • Split pull#19031 in smaller, digestible PRs, targeting each one to have 100% code coverage of modified code (see details on the PR page):
    • Preparation changes
    • Change CNetAddr::ip to have flexible size
    • Implement addrv2 (un)serializing
    • Advertise support for addrv2 and start sending such messages to peers
  • Document addrv2 next to addr (Document addrv2 and sendaddrv2 messages bitcoin-dot-org/developer.bitcoin.org#99)
• Implement Tor v3 on top of that (Complete the BIP155 implementation and upgrade to TORv3 #19954).

Related:
issue#2091 Binding to multiple anonymous networks (esp. I2P)
issue#9214 ensure ADD_ONION implementation is compatible with upstream changes, next generation onion addresses
issue#18254 setting externalip=<version 3 onion address> results in error