sara90wp

Hello! I’ve inspected your website and this is what I see on my side:

https://prnt.sc/8nl5ADTofbjb

If you still see duplicated ‘buy now’ button on some other pages, please try deactivating plugins one by one, in order to test whether some plugin you are using is causing the conflict.

*Please make sure to backup your website before deactivating plugins or theme, just to be on the safe side.

I hope this was helpful!

Hello! Please have a look at these articles that could be useful:

https://stackoverflow.com/questions/43425538/how-to-automatically-add-categories-sub-categories-in-wordpress-nav-menu

https://generatepress.com/forums/topic/automatically-add-posts-to-menu/

Regarding your third question – you would probably need to find some custom solution or test if this plugin works accordingly:

https://www.ads-software.com/plugins/automatically-update-permalinks/

I hope this helps!