PowerShell errors with "running scripts is disabled on this system"

Attempting to run rbxtsc in PowerShell results in an error like this:

This happens if PowerShell is not configured to run scripts downloaded from the internet (like roblox-ts).

You can allow this by running the following command in PowerShell as an administrator:

Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope CurrentUser

You can run PowerShell as an administrator by right-clicking the Windows logo in the bottom left corner and selecting "Windows PowerShell (Admin)"

More information here