I and at least one other person on the MacAdmins Slack saw situations in which a known working password (can log into the computer, can use
sudo to escalate privileges in the terminal) on an admin account is not working in System Preferences to unlock a prefpane. Special thanks to owen on the MacAdmins Slack for pointing us to this knowledgebase article: If you can’t unlock settings in System Preferences.
tl;dr: do an SMC reset. That should fix it.