Windows – How to change encryption from RC4 to AES in order to allow RDP to the remote servers

The first thing to check would be the timeout settings in Terminal Services Configuration. It's in the Sessions tab in the TSC.

Checking the Kerberos AES checkboxes for the users would cause authentication failures on pre-Vista clients. This is probably the reason that it's not set by default.

The Kerberos AES support checkboxes correspond to the value set in an attribute called msDS-SupportedEncryptionTypes

To change this for more than one user, you can utilize PowerShell and the ActiveDirectory module:

# The numerical values for Kerberos AES encryption types to support
$AES128 = 0x8
$AES256 = 0x10

# Fetch all users from an OU with their current support encryption types attribute
$Users = Get-ADUser -Filter * -SearchBase "OU=SecureUsers,OU=Users,DC=domain,DC=tld" -Properties "msDS-SupportedEncryptionTypes"
foreach($User in $Users)
{
    # If none are currently supported, enable AES256
    $encTypes = $User."msDS-SupportedEncryptionType"
    if(($encTypes -band $AES128) -ne $AES128 -and ($encTypes -band $AES256) -ne $AES256)
    {
        Set-ADUser $User -Replace @{"msDS-SupportedEncryptionTypes"=($encTypes -bor $AES256)}
    }
}