we have clients with older Safari Versions (5.1.7) and they can not see the products in our shop. I made this site with flexboxes. Is it possiple to manipulate the CSS or HTML that the clients can see the products?
I just double checked OS versions and feature sets. Your clients won’t be able to update to modern browsers since builds no longer include support for OS X Leopard. That OS is over nine years old.
Flex was only partially supported for that release.
I recommend you leverage the modernizr.com library and write custom CSS for feature sets not supported.
I would imagine they are having problems with many things they are trying to do. Like @webdev mentioned try getting them to use Chrome but I wonder how their machine would handle that.