Yes.
From the main menu of Valheim, there is a white button [Show Player.log] on the lower left.
Press the button and a file explorer window will open and you will find a text file called [Permittedlist.txt]

This text file is empty until you fill it.

One Steam ID per line with no other characters. Each of the player Steam ID's are whitelisted and can join world automatically and no password is needed for the server as ALL unlisted persons are default banned from the server.

I don't know yet how to whitelist an XBox crossplay player who has no Steam ID. I wish I knew.