Disable Password Expiration Azure AD

Connect-AzureAD
Set-AzureADUser -ObjectId <SyncACCOUNT>@<DOMAIN>.onmicrosoft.com -PasswordPolicies DisablePasswordExpiration

And if you want all online created accounts disable Password expiration:
Get-AzureADUser -All $true | Set-AzureADUser -PasswordPolicies DisablePasswordExpiration