Add a user to all channels including private channels in all Teams in Microsoft Teams

I need to add a user to all channels in all teams in Microsoft Teams.

I tried this:

Connect-MicrosoftTeams
$AllTeams = Get-Team

Foreach ($Team in $AllTeams)
{Add-TeamUser -GroupId $Team.GroupID -User USERS-EMAIL -Role Owner
Start-Sleep -Seconds 2}

And it adds them to the team but not all the channels, namely private channels.

Private channel membership is separate from Team membership; that's kind of the point of them being private; you don't want someone in a Team to have access to private channels within that Team automatically (even the owner of a Team doesn't automatically have access to any private channels, unless they create them or added to them). To add a user to a private channel requires the Add-TeamChannelUser command from the MicrosoftTeamsPowerShell module.

Use this line to add someone to a private channel of a specified team:

Add-TeamChannelUser -GroupId $Team.GroupID -User <USERS-EMAIL> -DisplayName <NAME OF CHANNEL> #New line

Adding someone to a private channel will complete within the PowerShell environment immediately but may take some time before that user shows up in the Teams client.