Microsoft Defender AV must control whether exclusions are visible to Local Admins.
Disabled (Default): If this setting is not configured or disabled, local admins can see exclusions in the Windows Security App or via PowerShell.
Enabled: If this setting is enabled, local admins no longer see the exclusion list in Windows Security App or via PowerShell.
Note: Applying this setting will not remove exclusions, it only prevents them from being visible to local admins. This is reflected in Get-MpPreference.
How this relates to the STIG checklist: STIG vs SCAP benchmark.