In this case let me present you with two of my demo apps that, when joined together, could be the solution you are looking for.
1 - Save Canvas image to GDrive
https://x.thunkable.com/projectPage/618cfa678cdb0f0011998dbe
2 - Read image file from device and display it in the screen.
https://x.thunkable.com/projectPage/61f68431c3761001dba12df1
When reading the image from device, I read it as Base64
and when saving an image to GDrive I get the image as Base64
so you can combine both to make your solution.
If you are developing in DnD then you only need one of my apps because DnD now has a file picker
component.
See the tutorial to save image to GDrive