I had trouble getting the debugger running about 6 weeks ago, posted a query, tried the suggestions, got no joy, got distracted by other tasks. Am now back at it.
I have deleted and recreated the debugger extension. I have deleted and reinstalled Postgres itself. (EDB Windows binary installer)
"The debugger plugin is not enabled. Please add the plugin to the shared_preload_libraries setting in the postgresql.conf file and restart the database server for indirect debugging."
The pgAdmin I am running is in C:\Program Files (x86)\pgAdmin 4\v4\runtime, however, EDB Postgres also installed an older version of pgAdmin4.exe (4.2) in C:\Program Files\PostgreSQL\9.6\pgAdmin 4\bin
Going to a command line, pg_ctl start complains
"$libdirplugin_debugger.dll": No such file or directory"
and shuts down Postgres. Yes, the missing "\" is exactly what is reported but NOT what is in the conf file.
If I hard code the path to plugin_debugger.dll it complains about that. I am not finding where $libdir is defined. I suspect the pgAdmin4 I am running is making assumptions that don't match the actual installed libdir path, and that moving that dll to the right place will solve the problem.
pg_config --libdir reports:
C:/PROGRA~1/POSTGR~1/9.6/lib
which is where plugin_debugger.dll is located (assuming the forward slashes, 8.3, etc. are translated correctly)