CISA, the NSA, and others released guidance to help critical infrastructure operators create inventories for their complex OT networks

Foundations for OT Cybersecurity: Asset Inventory Guidance for Owners and Operators | CISA
By following this guidance, organizations can enhance their overall security posture, improve maintenance and reliability, and ensure the safety and resilience

Cybersecurity and Infrastructure Security Agency CISA (www.cisa.gov)
NSA Joins CISA and Others to Share OT Asset Inventory Guidance
FORT MEADE, Md. - The National Security Agency (NSA) is joining the Cybersecurity and Infrastructure Security Agency (CISA) and others to release the Cybersecurity Technical Report (CTR),
National Security Agency/Central Security Service (www.nsa.gov)