Create a dummy RDP Application ('Hide from User' option checked) in PAM and associate that service with the Device Group:
Transparent Login option is now made available to the Device Group:
As the checking for Transparent Login configuration is at device level, the suggested workaround is practically bypassing this validation. Hence, the Transparent Login might be enabled on the Device Group level, but the Transparent Login configuration need to be done on device level.
Also, the suggested workaround is not suitable for 'Command String' Transparent Login.