A disagreement over the PostgreSQL trademark
This release on PostgreSQL.org describes an ongoing disagreement over the PostgreSQL trademark:

In 2020, the PostgreSQL Core Team was made aware that an organization had filed applications to register the 'PostgreSQL' and 'PostgreSQL Community' trademarks in the European Union and the United States, and had already registered trademarks in Spain. The organization, a 3rd party not-for-profit corporation in Spain called 'Fundación PostgreSQL,' did not give any indication to the PostgreSQL Core Team or PGCAC that they would file these applications.