I'm using the Media & Text block within Gutenberg. You can adjust the size of the image by dragging the small blue circle:
Looking at the Media & Text settings on the right, it doesn't look possible to select the image size.
When using the stand alone image block, you can adjust the image size, like so:
Is it possible to set an image size using a function for this block type? I need the design to be consistent on the front-end.