>I would love to customise my website further to my brand‘s needs with an individual, modern loading animation for the cart.

who’s stopping you ?
the cart deosn’t even do animations other than a loading gif when it’s updating (which is just simple css)

and – in any event – beauty is in the eye of the beholder , not too mention that I’ve also seen plenty of “beautified” wppizza carts that were so “beautiful” that i couldn’t even find the cart anymore an a site because it was hidden in some sort of icon in some corner somewhere

there are also plenty of shortcodes options that only let you show certain parts of the cart etc

you really are free to do what you like so am not sure how this is a “feature request”

essentially, there are various classes/ids that use the same background image that comes with wordpress for the “animations” (though sizes are being altered depending on where they are used, hence the different classes/ids )

i.e (somewhat simplified)

#wppizza-loading,.wppizza-loading,.wppizza-load, .wppizza-load-redirect,.wppizza-loading-small{
background-image:url('[path]/wp-includes/js/tinymce/skins/lightgray/img/loader.gif');
}

so you could simply override this background image with your own css/image as desired
(see also https://docs.wp-pizza.com/advanced/?section=frontend-css-styles-layout )