Welcome to the Shopify Community. I read your problem and it seems that I need to analyze your website to provide the solution here. Would you please share your website URL and if your website is password protected then also provide the password.
I am facing some more problems related to z-index in other elements of the website
On the homepage of my website (www.swayur.com) there are product sliders in that the problem is that I am not able to click the products fully on DESKTOP. Which means whenever my cursor pointer is between the two slider control buttons (left and right) then I can't click on the product. I need to keep the cursor above or below the two slider control buttons.
Visit the website and inspect the two buttons (right and left) you will understand the problem.