Installation Issue(Windows 10, Raw Therapee 5.8)

Well, you need to unzip the folder, maybe give it a shorter name, and run it from there. Mine are on an external drive.

The beauty of that method is that you can have several versions. So I have the release version, and also the latest DEV version parallel. And you can add ART too from this link, unzip (or un7z) and add a folder next to it:

https://keybase.pub/gaaned92/ART-W64NightlyBuilds/