I am in a process of upgrading postgres 12 to 13 on ubuntu. When I am running the test getting error could not load library "$libdir/plugin_debugger": ERROR: could not load library "/usr/lib/postgresql/13/lib/plugin_debugger.so": /usr/lib/postgresql/13/lib/plugin_debugger.so: undefined symbol: elog_finish
PostgreSQL extension should be compiled against one selected major release. So you cannot to use plugin_debugger for PostgreSQL 12 for PostgreSQL 13. You should to install plugin_debugger for PostgreSQL 13.