Whitelisted players, only has an effect when services.minecraft-server.declarative is true and the whitelist is enabled via services.minecraft-server.serverProperties by setting white-list to true. This is a mapping from Minecraft usernames to UUIDs. You can use https://mcuuid.net/ to get a Minecraft UUID for a username.
Declarations
Type
attribute set of Minecraft UUIDDefault
{ }Example
{
username1 = "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx";
username2 = "yyyyyyyy-yyyy-yyyy-yyyy-yyyyyyyyyyyy";
};