Update-Module: Module 'PnP.PowerShell' was not installed by using Install-Module, so it cannot be updated.

[nag433]

unable to update pnp.powershell

[nag433]

Update-Module: Module 'PnP.PowerShell' was not installed by using Install-Module, so it cannot be updated.

[ToddKlindt]

Run this PowerShell to see where it's installed:
Get-InstalledModule -Name pnp.powershell | select InstalledLocation
You can manaully delete that directory in Explorer. Then you should be good to go.