Right so this is exactly the kind of report that gets dismissed way too quickly. Big black cats in North America get written off constantly but the sightings are consistent enough across decades that theres clearly something going on. The Ozarks region specifically has had reports going back further than most people realise.
My gut says either escaped or released exotic pets that have established a small breeding population, or genuinely a melanistic cougar which mainstream zoology insists doesn't exist but which keeps getting reported anyway. The "melanistic cougar doesn't happen" argument feels increasingly shaky when you stack up how many independent witnesses describe the same thing.
What were the specifics of what you saw? Size relative to a dog, movement pattern, tail length. Those details matter a lot for ruling things in or out. A genuinely large black cat moves completely differently to a dog and most witnesses who've actually seen both know immediately which is which. You're probably not losing it, people tend to underreport these because they know they'll get laughed at.