Add folders to favorites but exclude from libraries?

I would imagine that this must be super simple – I did it before, but I’m having trouble remembering now.

What is the procedure for adding folders to favorites but excluding them from libraries? I remember to exclude them from library scans… but there’s something I’m forgetting when setting content. (Or maybe I shouldn’t be doing that part.)

For just one example, I’ll often store uncompressed videos on my external hard drive in a folder called “Uncompressed” due to space issues on my SSD, and I don’t want to officially “add” them to my library yet.

Thanks,

Alex