Craig Brookhart :
Isolated some relevant code lines for you. Not sure how succesfull copy/paste of code in this site is. Take care of '-' ... and backtick on line starting with $NewTeam. GUID == GUID from custom template on my development tenant, won't work for you (replace with a GUID from your own tenant). Prefill variables [string]$TeamName with name of your Team, [string]$Description and [string]$Visibility ('Private' or 'Public').
To be able to connect/run you need proper consent ($Result line is triggering this, see: https://docs.microsoft.com/en-us/graph/api/team-post?view=graph-rest-beta&tabs=http ... you'll need proper (Admin) rights to be able to do so.
Import-Module -Name 'Microsoft.Graph.Authentication' -Force
$Result = Connect-Graph -Scopes @("Group.ReadWrite.All", "Directory.ReadWrite.All")
Select-MgProfile -Name beta
$NewTeam = New-MgTeam -DisplayName $TeamName -Description $Description -Visibility $Visibility `
-AdditionalProperties @{
"template@odata.bind" = "https://graph.microsoft.com/beta/teamsTemplates('9f93256d-365b-43a8-9922-ac987e351726')"
}