There are some great communities of obsessive hobbyists here like !Selfhosted@lemmy.world, and if you throw a brick in any direction you’ll hit two Linux nerds, but reddit has /r/sysadmin and other infosec groups that have large numbers of industry professionals - and no amount of enthusiasm can substitute for real-world experience. I miss the conversation from people who spend time writing system security plans, reading NIST documentation for guidance, thinking about remote management for networks that support thousands of end users, and who have to actually deal with the cybersecurity incidents that get reported in the news.