Double url replacement in htacces?

Question

htaccess

Good afternoon! The crux of the matter is this.
There are 2 files:
index.html
index-cat=2.html
On the main index, does the link lead to index ? cat=2, i.e. in the line the link looks like mysite.com/index?cat=2.
I need to make sure that when accessing a link like index ? cat=2, information was taken from index - cat=2. html
But in order for the link in the browser line itself to be of the form - index ? cat=2
Of all that I tried, it turned out only to redirect to the html file.
I would be very grateful for help.

Answer 1

where does htaccess
firstly ?cart=2 is not a link and is not part of the url in principle
(from the point of view of mod_rewrite)
Secondly you need not .htaccess but AJAX