Yes, you can use Drag & Drop!
Universe for macOS* and iPadOS* features full drag and drop support with the Image and Text Blocks. To use Drag & Drop, simply drag the content from another app or website, right on to your Universe site in the Grid Editor.
What files types are currently supported?
For Images:
JPG
PNG
For Text Files:
TXT
RTF
*Universe for macOS requires Big Sur. Universe for iPadOS will still work on iPadOS 13, but requires iPadOS 14 to feature Drag & Drop support.