Google not ranks cms that's right. But the tech stack a cms is build on , that matters on seo.
Example: WP has old boring DB tech with PHP, deep internal link structure the googlebot not crawls, dynamic content same problem. And each new plugin you adding to your site is messing up your core code, do you think that google likes this?
Squarespace on the other side has; flat internal link structure, no plugins, a world-class cdn, a world-class tech DB with cockroach, and it has static content which always had an slight seo advantage over dynamic messed bloated content wp has. (from plugins).
Millions of people like that wp because it has plugins......
Which tech stack will be better for seo- what do you think?