With automatic sync on, your changes go back to Outlook about every 6 hours. Tick “Also bring in new contacts automatically” and new Outlook contacts come in too, at the level you pick (Acquaintance unless you change it).
Fix a person once on their Nimbus card — the sync carries it to Outlook.
Desktop Outlook that isn’t connected to Microsoft 365 can’t sync — use “Download a file for desktop Outlook” on the Sync page instead.