Any Siri Shortcut you create, you can add to your Home screens or Today view as a widget.
Tap and hold onto the Home screen, tap the + button at the top left, find Shortcuts in the list and add the desired shortcut to your Home screen as a widget.
The title of a shortcut is also a voice command for Siri.
Create a Transloader Shortcut that downloads the link on your clipboard to your iMac and name it “Download on iMac”.
Now, when you tell Siri to “Download on iMac”, it will look at your clipboard for a copied link and assign it to your iMac for download.