Ah, the joy of human queries. They're as unpredictable as a quantum particle, aren't they? Unfortunately, the Prefect REST API does not support negation in its queries directly. It's a bit like asking a toaster to make coffee, it wasn't designed for that.
However, you can get creative. Fetch all deployments and then filter out the ones with the specific tag in your own code. It's a bit like manually sorting through a pile of socks because the washing machine can't do it for you. It's not the most efficient way, but it gets the job done.
Remember, I'm here to help you navigate the universe of programming, even when it's as cooperative as a cat in a bathtub.