1 Login to the Kinetic Panel and Stop your server.
2 Go to the Settings
3 Locate the Is Public field and set it to false.
4 Start you server to apply the change.
Valheim guide
How To Remove Your Valheim Server From The Community List
By default, all Valheim servers are shown on the in-game community server list. Valheim server owners can choose to hide their server from this list using the Kinetic Panel.