Gets a list of sign-ins that use older versions of TLS. This can be queried using either PowerShell or by querying log analytics. Learn more about AAD TLS deprecation today https://docs.microsoft.com/en-us/troubleshoot/azure/active-directory/enable-support-tls-environment?tabs=azure-monitor#overview-of-new-telemetry-in-the-sign-in-logs

Get-LowTls.kql

// Interactive sign-ins only
SigninLogs
| where AuthenticationProcessingDetails has "Legacy TLS"
    and AuthenticationProcessingDetails has "True"
| extend JsonAuthProcDetails = parse_json(AuthenticationProcessingDetails)
| mv-apply JsonAuthProcDetails on (
    where JsonAuthProcDetails.key startswith "Legacy TLS"
    | project HasLegacyTls=JsonAuthProcDetails.value
)
| where HasLegacyTls == true

// Non-interactive sign-ins
AADNonInteractiveUserSignInLogs
| where AuthenticationProcessingDetails has "Legacy TLS"
    and AuthenticationProcessingDetails has "True"
| extend JsonAuthProcDetails = parse_json(AuthenticationProcessingDetails)
| mv-apply JsonAuthProcDetails on (
    where JsonAuthProcDetails.key startswith "Legacy TLS"
    | project HasLegacyTls=JsonAuthProcDetails.value
)
| where HasLegacyTls == true

Get-LowTls.ps1

# Pre-requisites
# Install-Module Microsoft.Graph

$tId = "nnnnn" #tenant ID
$agoDays = 4 #will filter the log for $agoDays from current date/time
$startDate = (Get-Date).AddDays(-($agoDays)).ToString('yyyy-MM-dd') #calculate start date for filter
$pathForExport = "./" #path to local filesystem for export of CSV file

Connect-MgGraph -TenantId $tId -Scopes "AuditLog.Read.All" #could also use Directory.Read.All
Select-MgProfile "beta" #Low TLS available in MS Graph preview endpoint

$signInsInteractive = Get-MgAuditLogSignIn -Filter "createdDateTime ge $startDate and (authenticationProcessingDetails/any(x:x/key eq 'legacy tls (tls 1.0, 1.1, 3des)' and x/value eq '1'))" -All
$signInsNonInteractive = Get-MgAuditLogSignIn -Filter "createdDateTime ge $startDate and signInEventTypes/any(t: t eq 'nonInteractiveUser') and (authenticationProcessingDetails/any(x:x/key eq 'legacy tls (tls 1.0, 1.1, 3des)' and x/value eq '1'))" -All

$signInsInteractive | Foreach-Object {
    foreach ($authDetail in $_.AuthenticationProcessingDetails)
    {
        if(($authDetail.Key -match "Legacy TLS") -and ($authDetail.Value -eq "True")){
            $_ | select CorrelationId, createdDateTime, userPrincipalName, userId, UserDisplayName, AppDisplayName, AppId, IPAddress, isInteractive, ResourceDisplayName, ResourceId 
        }
    }

} | Export-Csv -NoTypeInformation -Path ($pathForExport + "Interactive_lowTls_$tId.csv")

$signInsNonInteractive | Foreach-Object {
    foreach ($authDetail in $_.AuthenticationProcessingDetails)
    {
        if(($authDetail.Key -match "Legacy TLS") -and ($authDetail.Value -eq "True")){
            $_ | select CorrelationId, createdDateTime, userPrincipalName, userId, UserDisplayName, AppDisplayName, AppId, IPAddress, isInteractive, ResourceDisplayName, ResourceId 
        }
    }

} | Export-Csv -NoTypeInformation -Path ($pathForExport + "NonInteractive_lowTls_$tId.csv")

Any idea why I'd get an Get-MgAuditLogSignIn Get-MgAuditLogSignIn_List: Method not found
Here's a debug view of it. Not sure if I don't have a pre-req or am missing a step.

Running latest Powershell 7.2 and VSCode.

Love that you shared this here (and on Twitter, thanks)!

Try updating the Graph module to the latest version and restarting the PowerShell session.
Update-Module Microsoft.Graph