Accessing the Label tab on the Layer Properties dialog box in ArcMap is slow

Description

Accessing the Label tab on the Layer Properties dialog box in ArcMap is slow, taking several minutes for the dialog box to display.

Cause

This issue is related to following bug which has been fixed in 10.7, and also have patches for older versions.
BUG-000113336: Dialogs that include the font picker control, including the Layer Properties, Options, Character Marker Editor, and Label Manager open very slowly.

Workaround

• Upgrade to 10.7.x or, 
• If unable to upgrade to 10.7.x, it is recommended to apply the appropriate patch for the version in use: ArcGIS Desktop Dialog Initialization Performance Patch