Hi Kanna,
You could just insert an iframe into dashboard as what you did.
Possible reasons for what your iframe not showing would be that you had added some website which doesn't permit to be included inside an IFrame.(such as Google.com,
it depends on external website security policy).
You could use iframe to display web resource inside crm or websites which are supported to be included in iframe.
Please share me your business requirement on iframe or screenshot of iframe properties configuration if possible.
Regards,
Clofly
