Hey there! This is a great question!
At this time there’s no way to disable SAML/SSO for a single account. When SAML is enabled, this tells New Relic to use this the SAML authentication process for all users. However, for what you’re wanting you could embed those Insights charts within the dashboard to an external webpage and view them from there. This would circumvent you from having to create a single user with no SAML credentials as you could use any other user with access to that specific dashboard. You can find out a bit more about this here:
One thing that’s important to note is that you won’t be able to embed a dashboard itself, but you can embed each individual chart within the dashboard and recreate the layout of the dashboard on your webpage.
I hope this points you in the right direction!