Add all users except guest account as a Sharepoint online site viewer access

 

$SiteURL = "https://test.sharepoint.com/sites/team"
Connect-PnPOnline -Url $SiteURL -UseWebLogin
$Group = Get-PnPGroup -AssociatedVisitorGroup
$User = "Everyone except external users"
Add-PnPGroupMember -LoginName $User -Identity $Group