There was an enormous amount of effort and thought put into the making of Spiral to have it NOT be Saw IX. A lot of the choices made are actually discussed throughout the Spiral wiki page.
In addition, Spiral was also not meant to be a complete reboot. There still may be a Saw 9, and may also be a sequel to Spiral.
Finally, it also is not a reimagination. It is simply a similar movie where the antagonist is a Jigsaw copycat, and which utilizes the theme of traps giving the victims the choice of death versus voluntary dismemberment/disfigurement/disablement.
In my opinion, as a long time Saw franchise 'fan', Spiral is quite able to be appreciated as a stand-alone movie, however a viewer would better understand the traps if one or two of the original series were previously viewed. It is definitely not a requirement to view all previous 8 movies in the franchise to understand Spiral.
If, as you say, you've seen previous movies in the series, you are perfect as a viewer of this new one. You'll 'get' the concept of the traps and not be completely lost in the why of things.
My last comments here will be completely personal opinion, not that the rest was anything other, but still... I am not a fan of Chris Rock. He's always been annoying to me. It's mostly his (in my opinion) kind of whiney voice and delivery. However, in this one, for some reason, I was never bothered by it, at all. It really was a nice job of branching out into a new genre as an actor and he did a fairly remarkable job.