Can you upgrade the osx from app store running from an external ssd

Hi there.

I am currently on El Capitan 10.11.6 on my Macbook Pro and would like to test out Mojave 10.14 on an external drive. Unfortunately an app I have been using forever is not supported upgrading to Mojave and I want to test some things out before committing to upgrading my Macbook.

Firstly I have made a carbon copy clone of my system onto an external ssd. I can now boot up my clone system ssd to test things from.

My question is:

Can I boot from the external ssd and run the Mojave upgrade from the app store to update the mac os on the external ssd without causing any problems to my main Macbook pro system?

Any info on this would be great before I try anything.

Thanks so much

Bruce