Zend certified PHP/Magento developer

Error 404 on a specific product page

Magento 2.4.2-p1
Smartwave Porto theme
Amasty extensions

I have a product on the front page and when I click on it, I get the Magento 404 page (my store’s header and footer and in the body 404 on our background).

Why does this happen and how to fix? I have compared the product URL and it appears to be correct. What role does the .html play?