Add-WindowsCapability fails with "Source files could not be found"

I am trying to install RSAT on some Windows 10 systems that have no internet connectivity. Two of the Windows 10 systems are 20H2, and one of them is 21H2. All three have the same problem. To install the RSAT tools for an offline system, I found this link: https://michlstechblog.info/blog/windows-installing-rsat-tools-online-or-offline/

I used this link to determine where/how to get the FoD DVD ISO file: https://docs.microsoft.com/en-us/windows-hardware/manufacture/desktop/features-on-demand-v2--capabilities?view=windows-11 Maybe part of the problem is that the FoD DVD is from Windows 10 2004 build, but there is not a newer version that I can find on my.visualstudio download section. I manually checked other builds of Windows 10 (searching for "Feature on Demand" doesn't find anything).

When I do the "get-windowscapability", it seems to read the source properly:

 C:\WINDOWS\system32> Get-WindowsCapability -Name "RSAT*" -Online -LimitAccess -Source "E:\" | Foreach-object {write-host $_.Name}
Rsat.ActiveDirectory.DS-LDS.Tools~~~~0.0.1.0
Rsat.BitLocker.Recovery.Tools~~~~0.0.1.0
Rsat.CertificateServices.Tools~~~~0.0.1.0
Rsat.DHCP.Tools~~~~0.0.1.0
Rsat.Dns.Tools~~~~0.0.1.0
Rsat.FailoverCluster.Management.Tools~~~~0.0.1.0
Rsat.FileServices.Tools~~~~0.0.1.0
Rsat.GroupPolicy.Management.Tools~~~~0.0.1.0
Rsat.IPAM.Client.Tools~~~~0.0.1.0
Rsat.LLDP.Tools~~~~0.0.1.0
Rsat.NetworkController.Tools~~~~0.0.1.0
Rsat.NetworkLoadBalancing.Tools~~~~0.0.1.0
Rsat.RemoteAccess.Management.Tools~~~~0.0.1.0
Rsat.RemoteDesktop.Services.Tools~~~~0.0.1.0
Rsat.ServerManager.Tools~~~~0.0.1.0
Rsat.Shielded.VM.Tools~~~~0.0.1.0
Rsat.StorageMigrationService.Management.Tools~~~~0.0.1.0
Rsat.StorageReplica.Tools~~~~0.0.1.0
Rsat.SystemInsights.Management.Tools~~~~0.0.1.0
Rsat.VolumeActivation.Tools~~~~0.0.1.0
Rsat.WSUS.Tools~~~~0.0.1.0

But when I try "add-windowscapability", it says it cannot found the source files:

C:\WINDOWS\system32> Get-WindowsCapability -Name "RSAT*" -Online -LimitAccess -Source "E:\" | Foreach-object {Add-WindowsCapability -Name $_.Name -Online -LimitAccess -Source "E:\" }
Add-WindowsCapability : The source files could not be found. 
Use the "Source" option to specify the location of the files that are required to restore the feature. For more information on specifying a source location, see 
https://go.microsoft.com/fwlink/?LinkId=243077.
At line:1 char:90
+ ... ach-object {Add-WindowsCapability -Name $_.Name -Online -LimitAccess  ...
+                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [Add-WindowsCapability], COMException
    + FullyQualifiedErrorId : Microsoft.Dism.Commands.AddWindowsCapabilityCommand
 
Add-WindowsCapability : The source files could not be found. 
Use the "Source" option to specify the location of the files that are required to restore the feature. For more information on specifying a source location, see 
https://go.microsoft.com/fwlink/?LinkId=243077.
At line:1 char:90
+ ... ach-object {Add-WindowsCapability -Name $_.Name -Online -LimitAccess  ...
+                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [Add-WindowsCapability], COMException
    + FullyQualifiedErrorId : Microsoft.Dism.Commands.AddWindowsCapabilityCommand

C:\WINDOWS\system32> Get-WindowsCapability -Name "RSAT*" -Online -LimitAccess -Source "E:\" | Add-WindowsCapability -Online -LimitAccess -Source "E:\"
Add-WindowsCapability : The source files could not be found. 
Use the "Source" option to specify the location of the files that are required to restore the feature. For more information on specifying a source location, see 
https://go.microsoft.com/fwlink/?LinkId=243077.
At line:1 char:74
+ ... urce "E:\" | Add-WindowsCapability -Online -LimitAccess -Source "E:\"
+                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [Add-WindowsCapability], COMException
    + FullyQualifiedErrorId : Microsoft.Dism.Commands.AddWindowsCapabilityCommand
   

I also checked the log files (C:\Windows\Logs\DISM\dism.log) and it shows the same error there. Any ideas how to get this to work? Thanks in advance.