[IdiotSavage]

PowerShell is not really that much more verbose. This is the equivalent of the nushell command by crabsand.

  dir | ? LastWriteTime -lt (Get-Date).AddDays(-21) | del

[metaltyphoon]

Too much casing changes, IMO

[IdiotSavage]

Sorry. Fixed it for you.

  dir | ? lastwritetime -lt (get-date).adddays(-21) | del

PowerShell is not case sensitive (but nushell and bash are).