This is a new major release of Namecoin Core. It contains all of the updates done in upstream Bitcoin Core 0.19.0, minor improvements to the Namecoin code, and the following Namecoin-specific user visible change:
The mempool now allows multiple updates of a single name (in a chain of transactions). This is something that is allowed in blocks already, i.e. it is just a policy change. The
name_update RPC command still prevents such transactions from being created for now, until miners and relaying nodes have updated sufficiently. More details can be found in #322.