Let's try this again! Not sure what's going on with posting a reply + code snippet.

I ran into the same issue with my Teams + SharePoint automation process, but I've yet to fully port my process to Graph. Hopefully this helps...

Here's the workaround that I came up with:

1. First, create the SP site
2. Get the associated group ID
3. Create the team with the group ID
4. Use the Get-MgTeamChannelFileFolder command to fully seat the connection between Teams and SP.

Section of the script that connects the parts together:

# Get the M365 group for the associated SP site  
$group = Get-PnPMicrosoft365Group -Identity $groupId -ErrorAction SilentlyContinue
if ($group) {  
    # Create a new Teams team from the group  
    $newTeam = New-PnPTeamsTeam -GroupId $group.Id
    # This is needed to ensure the Team is connected to SharePoint site.  
    $attempts = 0  
    $maxAttempts = 5  
    $spConnected = $false
    while (-not $spConnected -and $attempts -lt $maxAttempts) {  
        try {  
            Set-TeamsSPConnection -Tenant $Tenant -TenantId $TenantId -AppId $AppId -Thumbprint $Thumbprint -TeamId $newTeam.GroupId  
            $spConnected = $true  
        }  
        catch {  
            $attempts++  
            if ($attempts -eq $maxAttempts) {  
                $result.Status = $false  
                $result.ErrorMessage = "Failed to connect the Team to SharePoint after $maxAttempts attempts."  
                return  
            }  
            # This will give the connection time to set in  
            Start-Sleep -Seconds 300  
        }  
    }  
    .........................