Bitcoin Core 29.0 removes UPnP support. Its release notes direct users who need automatic port mapping to the natpmp option, which selects PCP or NAT-PMP according to router support.
The project also replaced an external library with a built-in implementation. Another change derives the default onion listening port from a custom port setting, addressing conflicts when several local nodes use different ports.
These changes matter to configuration and connectivity, rather than the basic meaning of a Bitcoin transaction. This is an archive account of the 29.0 notes. The source includes migration details that should be read in context with the documentation for the version actually in use.