AC-4(21) Information flow | physical or logical separation of information flows
What the standard requires
Separate information flows logically or physically using [organization-defined mechanisms and/or techniques] to accomplish [required separations].
Quoted verbatim from NIST SP 800-53 Rev 5 (OSCAL catalog), which is in the public domain.
Cross-framework mappings
No cross-framework mapping is seeded for this control. That is stated rather than filled in: a mapping nobody authored is worse than a gap you can see.
Track AC-4(21) with evidence behind it
In CMDash this control is a row with an owner, a status, uploaded evidence kept with its full history, and an export an assessor can read.