Hello,
1/ Go to Single Product Builder and add the Short description element to the content of the page https://prnt.sc/X5zYhv2SOuGD , or disable the Single Product Builder.
2/ I do not see it on the product page now. Have you sorted it out?
3/ Theme Options > Mobile panel > Enable Mobile Panel, then edit sections https://prnt.sc/XVuwqlzxOk_f
4/ Please watch this video – https://youtu.be/LgzC4iK-j6A
5/ There is no such option, by default for the Products element.
Try – https://prnt.sc/nsphANZ4_R2P
6/ Please provide FTP access.
Regards