(EDIT for JHF 26 version; the original was the JHF 54 version)
Found it.  Here's the package:
 
 
[Expert@cpmgmt01:0]# da_cli packages_info |jq -r '.packages[]|select(.packageKey|contains("BUNDLE_R81_20_JUMBO_HF_MAIN_SC"))'
{
  "availableFrom": "2024-04-07 00:00:00",
  "blocksUninstall": false,
  "broughtVersion": "6.0_5_4",
  "build": 54,
  "category": "capability",
  "description": "<p>SmartConsole R81.20 version is compatible with any R81.20 Security Management server. </p><p><strong>SmartConsole automatically updates to the latest Build, as long as you have an Internet connection. The update is rolled out gradually and should be completed within 1 week. It is not necessary to download and install newer builds manually</strong></p>",
  "displayName": "R81.20 SmartConsole Build 653",
  "fileSize": "436179034",
  "filename": "Check_Point_SmartConsole_R81_20_jumbo_HF_B653_Win.tgz",
  "hasMetadata": true,
  "htmlReportExists": false,
  "installCritical": false,
  "isBlinkImage": false,
  "isHfa": true,
  "isInRepository": false,
  "md5": "76e12ddf2ac8ea2657057b61647bc76a",
  "order": 0,
  "packageKey": "CheckPoint#CPUpdates#All#6.0#5#4#BUNDLE_R81_20_JUMBO_HF_MAIN_SC#54",
  "packageOrigin": "Download Center",
  "packageType": "Wrapper",
  "product": "CPUpdates",
  "requiresReboot": false,
  "state": "Available for download",
  "version": "6.0"
}
 
 
But you need the JHF 26 version which was Build 646.  You need the package named Check_Point_SmartConsole_R81_20_jumbo_HF_B646_Win.tgz and you should be ok:
From Expert mode:
 
da_cli add_private_package package=Check_Point_SmartConsole_R81_20_jumbo_HF_B646_Win.tgz
da_cli download package=Check_Point_SmartConsole_R81_20_jumbo_HF_B646_Win.tgz 
da_cli verify package=package=Check_Point_SmartConsole_R81_20_jumbo_HF_B646_Win.tgz 
da_cli install package=Check_Point_SmartConsole_R81_20_jumbo_HF_B646_Win.tgz  reboot_delay=60