Unable to log in to Messages on Mac

I use Messages on an iPhone, iPad, and up until a couple of days ago my Mac without any issues. However, starting about 2 days ago, Messages on my Mac abruptly stopped working. It no longer allows me to sign into my iCloud account in Messages on Mac, I either get a persistent spinning circle or "An unknown error occurred."

And yes I have seen this link, I already tried everything there and it did not work.