Color Contrast rules for WCAG2.0 And WCGA2.1 giving incorrect result.

I am using axe-core library in node js with playwright.

Details:-

Install [Node.js](https://docs.npmjs.com/getting-started/installing-node) if you haven't already.

Install Playwright: npm install playwright

Install @axe-core/playwright: npm install @axe-core/playwright

v4.10

I have below questions.
1.What default rule Axe-core uses to scan the website for accessibility ?

Issue:-
2.When I am using axe core to scan web page I noticed that It is giving issue for Color contrast.
It is showing expected color contrast should be 3, but it found 1.9.2 and apart from this I got other issues as well.
I have concern about this[I read some where in article that Default scan tag used by axe core is WCGA2.0, is that correct? if yes then is that color contrast rules are different form WCAG2.0 & WCAG2.1? if yes then what is the different?]
And same when I scan the page using tags "wcag22aa","wcag21aa",then my page does not show any accessibility issues.

Now I wanted to understand this, what happens why it gave error with default scan and why not with wcag22aa","wcag21aa" tags?
What does it mean?

3.How accurate the scan results is with axe-core? in terms of %.

4.Can we take it as 100% accessibility free it it passes certain scan rule?