If I add an image block like the one above, I can link to the image.
Clicking the image will then load the full-sized image in the browser window. You can try on the main one above. one above.
If I want to make this a little more elegant I can convert the image to a gallery. The link will then open in a lightbox.
To convert the image block all I need to do is select the image, click on the image icon on the Block Toolbar and choose Transform to Gallery:
Here is a animation showing the result. You can also just click the image in a lightbox above.