There is no that option. Product showing number is same on desktop and mobile device.
If you want to change the product number on mobile, please duplicate the product section and set the different "Product per page" value.
And then, please hide one on mobile and hide the other one on desktop.
This is the best way.
If you have any other questions, please let us know again without hesitation.
And we'll be thankful, if you leave 5 stars and feedback to our theme.
Best Regards, C-Themes