I didn't realize the greatness of GOG. Is it still possible to transfer Steam Witcher and cyberpunk keys to GOG?

Still? To the best of my knowledge, it was never possible to directly transfer Steam games to a GOG library.
There was once "GOG connect", if that's what you are referring to, but no, that is no longer available.

How is a customer supposed to realise the existance of such haphazardly scattered information, unless through personal experience? That back-up of the Witcher beginning 2012, for example, gets buried in search engine results unless one knows what to search for, i.e. including the specific term "back up" rather than say "(steam) key", or even "free". We all benefit from your seemingly limitless and encyclopedic knowledge...

It's effectively a past campaign that has ended, since only games redeemed more than 2½ years ago are eligible. Even then, the requirement of a product key suggests it only applies to copies bought through a third party. I can't blame them for not putting the link somewhere visible. LOL. Thank you. It was more of a "Did you know...?" type of post rather than something with practical use.