Can I customize the URL of a file/folder I want to share?

Yes. Click on the Share button next to a file/folder and select Send Link. A new window will pop-up. You can customize the link URL by clicking on the pencil icon on the right side of the link, type in the wanted name of the link URL and click Done. No special characters and spaces are allowed. Confirm it by clicking on Ok in the bottom of the pop-up window.