Powershell Error Re: M$ Advice Thread (Windows 10 Start Menu Suddenly very slow. Also Firefox (not other browsers) Fresh 'Reset' of Windows

I had to 'Reset' my Windows and I opted to 'keep my files'. I did Disk Cleanup to remove the old.windows files.

Before I had the problem, Windows was extremely snappy and quick even after a year or more of being installed. The problem was caused after I installed an app made by ASRock which was able to play with clock values etc and it completely bugged my machine so I couldn't use it, I found it easiest to try a reset of Windows.

Long story short, it is slow now BUT only when clicking the Start Menu and/or searching for app etc in taskbar. Everything else is quick. Temps are perfect, games run perfectly, 4k video etc etc.

I read this thread: https://answers.microsoft.com/en-us/windows/forum/windows_10-start-winpc/start-menu-wont-open-windows-10-is-suddenly/4ea92f23-5680-4d3e-93a8-4c0aa7bc49b7

It basically got me to type this into Powershell:

Get-AppXPackage -AllUsers |Where-Object {$_.InstallLocation -like "*SystemApps*"} | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register "$($_.InstallLocation)\AppXManifest.xml"}

He says if this process fails, I either typed incorrectly or have a LARGE problem with Windows. Seeing as I've typed/pasted this several times, and I downloaded Windows directly from Microsoft, I don't see what I can do next. I receive this error in Powershell telling me that I need to close Windows Client and WindowsStartMenu (or something...):

ERROR: 
Add-AppxPackage : Deployment failed with HRESULT: 0x80073D02, The package could not be installed because resources it   modifies are currently in use.                                                                                          error 0x80073D02: Unable to install because the following apps need to be closed                                        Microsoft.Windows.StartMenuExperienceHost_10.0.19041.610_neutral_neutral_cw5n1h2txyewy.                                 NOTE: For additional information, look for [ActivityId] 46500a1d-382a-0000-e571-56462a38d701 in the Event Log or use    the command line Get-AppPackageLog -ActivityID 46500a1d-382a-0000-e571-56462a38d701                                     At line:1 char:94                                                                                                       + ...  | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register "$($_.I ...                                         +                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~                                                 + CategoryInfo          : NotSpecified: (C:\Windows\Syst...ppXManifest.xml:String) [Add-AppxPackage], Exception         + FullyQualifiedErrorId : DeploymentError,Microsoft.Windows.Appx.PackageManager.Commands.AddAppxPackageCommand                                                                                                                              Add-AppxPackage : Deployment failed with HRESULT: 0x80073D02, The package could not be installed because resources it   modifies are currently in use.                                                                                          error 0x80073D02: Unable to install because the following apps need to be closed
MicrosoftWindows.Client.CBS_120.2212.551.0_x64__cw5n1h2txyewy.
NOTE: For additional information, look for [ActivityId] 46500a1d-382a-0006-577e-51462a38d701 in the Event Log or use
the command line Get-AppPackageLog -ActivityID 46500a1d-382a-0006-577e-51462a38d701
At line:1 char:94
+ ...  | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register "$($_.I ...
+                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (C:\Windows\Syst...ppXManifest.xml:String) [Add-AppxPackage], Exception
    + FullyQualifiedErrorId : DeploymentError,Microsoft.Windows.Appx.PackageManager.Commands.AddAppxPackageCommand

Creating a new user account made everything work correctly and fast again.

Strange that this was necessary on a fresh 'reset' install of Windows, but at least this has fixed it.