I’ve used Scratch quite a bit as well and also teach both Scratch and Thunkable. I moved to Thunkable from GameSalad which was a no-code editor that worked really well for making games. The physics engine was great, you could easily manipulate sprites, etc. It also did not have a built-in graphic editor, however, besides rudimentary shapes (rectangles, circles and lines).
Thunkable does not have a way to create graphics internally so you will need to import them. I have used plenty of PNG files as buttons or images. I haven’t done a lot with sprites so I don’t know if there’s an issue with PNG files there. I would not expect Thunkable to handle SVG files well.
I’m a huge proponent of Thunkable. I’ve been around here a couple years and I’ve found it to be powerful and flexible in ways that other similar tools are not. GameSalad had many limitations (lack of easy-to-use cloud based data sources) and a diminishing user base.
But the one thing I cannot recommend about Thunkable is the Canvas component. I find it clunky, counter-intuitive and buggy. I have yet to see more than one or two examples of very basic games that work in Thunkable. I’d like to see it overhauled completely!