LRC installation in External Drive

In Windows-  The CC Desktop App and Lightroom-Classic will only install in the default  { C:\Program Files } folder, however the Catalog (.LRCAT) with the Previews (.LRDATA), and all image files can be stored and used on any connected hard-drive (internal or external)

This is similar to using a "Self Contained Catalog" as described in this article-

Catalog on multiple computers?

And moving a Catalog is relatively easy if done correctly-

Move Your Lightroom Catalog | Laura Shoe's Lightroom Training Tutorials and Tips 

Move Your Lightroom Photos to a New Hard Drive | Laura Shoe's Lightroom Training Tutorials and Tips

In Mac OS- a Mac user might answer the 'install' question, but again, Catalog and photos can be on an external drive.