I’m not sure if you are in the same boat, but I bought ARMA 2 and Operation Arrowhead many years back directly from the dev’s website. I logged into their site about a year ago, copied the registration keys, pasted them into Steam, and was able to redeem it through Steam directly. If your games have CD keys, Steam can oftentimes accept those directly like you are entering a Steam product key. I think you put it into the field where you enter Steam gift cards and product keys.
I have a “This is Fine” dog Funko Pop on my desk at work. He works well for rubber ducky programming, and he encapsulates the feelings I typically have after dealing with some of my clients.
This isn’t my picture, but it’s a similar setup: