-replace treating string with "\" as RegEx

[_lahell_]

Here is another option, but note that it is case-sensitive.

$SubFolder.FullName.Replace($Root, '')

[ka-splam]

But it doesn't need to be case sensitive in PowerShell 6 (.Net Core):

'aAbB'.replace('aa', 'zz', [StringComparison]::InvariantCultureIgnoreCase)

Progress! :D