Here are the steps that normally work
1. Install osquery
2. copy extension into the osquery folder
3. change the flags file and osquery.config with that is provided in github. (Make sure all the paths in the flags file are looking good)
4. Adjust the flags file for the logger to be tls and point it to your fleet DM (along with certs) but leave the config to be filesystem so that the local copy of osquery.conf comes into play (with queries for tables extended by extension)
5. restart the osquery service
At this point, osquery should load the extension and the config from osquery.conf should be read giving you the results on fleet DM