You beat me to it!

Thanks a lot !!! works perfectly!! Do I have to re-run this workflow whenever I restart the macbook?

@Render, No, it is now automatic. BTW I need to update this because this will not move a folder that's saved to Downloads by will move it's contents. Will update the answer in a few minutes.

Oh I didn't test it with a folder. I also made a separate script that creates an alias in the original system's download folder, so that I keep using the system folder for reference but everything is actually stored in the external drive. Is there a cleaner/more efficient way to do this?

You asked, "Is there a cleaner/more efficient way to do this?", you're going to have to define what's "cleaner/more efficient" for you.

Maybe there is a way to combine both scripts together rather than have two separate work flows, or use something other than alias to avoid having a shortcut arrow on the icons. (thanks for the folder update above)

@Render, "combine both scripts? What scripts are you talking about? I've not presented you with any scripts, this is an Automator Folder Action workflow that is not using any scripts, i.e. no Run AppleScript action or Run Shell Script action.

@user3439894 I meant workflow not script

@Render, Sorry, but I'm not understudying what you're asking. This may not be a perfect solution to what you ultimately wanted, but it's a good workaround,

I created another workflow and it's not working constantly : Get Folder Contents > Find Finder items in Download (external disk) > New Aliases in Downloads (system folder) .. but the files don't always create an alias like I want to. For example, if I download something from Safari, this workflow wouldn't work, it saves the original copy in both folders.

@Render, I've update my workflow to create an alias for each moved file. It comes after the Move Finder Item action. There is no need to use two separate workflows.

@Render, I also added a Kind is other alias to the Filter Finder Items so it doesn't create an endless loop.

Thanks a lot!!

I don't know if you're up for it, there is one last thing left if you are interested to tackle it, otherwise I can ask another question.

Shortcuts do not show as preview icons :

Any idea of a workaround to this?