synchronizing external USB Photo Drive to Photos App on Imac

[petalino]

So I decided to create a new slideshow using YouTube Slideshow Creator, but unfortunately
they removed this function.
Very disappointing!
Here are some of my past Youtube Slideshows created within YouTube:

Now I am searching for an alternative solution to create slideshows on my Mac directly and downloading them to Youtube.

It seems that the Mac Photos App could be a simple solution to achieve this, but I do not store any of my photos in the Photos App; they are all stored on an external USB drive.

Here is my question:

Can I sync my entire external USB drive containing photos - with the the Photos App,
so I do not have to leave Photos App in order to import individual photos to create a slideshow in Photos App?

Additionally I do not want to perform a full content transfer of my Gigantic Photo Drive to my Imac just to browse my pics with the Photos App; I just want to access them from within the Photos App without clogging up my IMac HD with terrabytes of photos, which are already stored on the external USB drive.

 

[petalino]

Just wondering if anyone has ideas about my issue?

 

[wilberforce]

I don't know the answer to your question, having not tried it myself, but this may be helpful:

Change where your files are stored in Photos on Mac

In Photos on your Mac, store photos in a photo library or outside of it. Copy external files into a Photos library.

support.apple.com