NIST
NIST SP 800-57 Part 1 Rev. 5 sets out how cryptographic keys should be managed across their life-cycle and recommends minimum key strengths. PKI-as-a-Service follows it by using at least 112-bit security strength (for example RSA 3072 or ECDSA P-256 and higher for new CAs), SHA-256 or stronger for signatures, and defined crypto-periods for each CA.
NIST SP 800-53 Rev. 5 is a catalogue of security controls. The PKI-related controls are SC-12, SC-13, SC-17 and IA-5(2).
NIST Cybersecurity Framework 2.0 groups outcomes into Govern, Identify, Protect, Detect, Respond and Recover. Certificates support Protect (identity and data security), and the portal's monitoring supports Detect.