Hi, @Deniz2 !
Is Google Drive the only viable option? If you are open to a slightly different approach, Approval Studio may help! It has a file uploader option that automatically sends the image that the customer uploaded in the shop as a reference file to the Approval Studio project. Then, artists can download it from there and use it however they like, with no quality reduction. And later you can even let your customers approve the design before it gets sent to them)