Hi,
With the 4.4.0, we added the support of Joomla 4, and with it, we also removed the old "add to cart legacy" and "checkout legacy" settings of the HikaShop configuration.
So if you were using them because of old view customizations, you are now using the new add to cart and checkout systems (which were added with the 3.0.0, so they've been legacy for several years now) and thus you need to redo the customization for the new views used by them.
Adding view customization is still working the same as before and no one reported any problem with it since the 4.4.0 was release. So if you have a problem with the creation of view overrides, it's probably something linked to your server setup (files/folders not writable, or security mechanism preventing the reception of the modified PHP code by the server).