Hi James,
I would recommend taking a look at this documentation:
Trusted root certificate profiles for Microsoft Intune
https://learn.microsoft.com/en-us/mem/intune/protect/certificates-trusted-root
When using Intune to provision devices with certificates to access your corporate resources and network, use a trusted certificate profile to deploy the trusted root certificate to those devices. Trusted root certificates establish a trust from the device to your root or intermediate (issuing) CA from which the other certificates are issued.
You deploy the trusted certificate profile to the same devices and users that receive the certificate profiles for Simple Certificate Enrollment Protocol (SCEP), Public Key Cryptography Standards (PKCS), and imported PKCS.
To create a trusted certificate profile
If this is helpful please accept answer.