Use the Image block to insert a single image onto your page or post.
Get started by clicking the + Inserter icon at the bottom-left corner of the screen and select the Image Block from the blocks list
Once you add the block you can then tap on the arrows to move the block up and down and on the ADD IMAGE option and select where you would like to add the image from
Once you selected the image you can then tap on the ellipse menu to either replace the image with another one or edit the image you added
You can also tap on the cogwheel icon to access the image settings where you can add a link to the image so it redirects the reader to another page or an external site, you can change the size of the image, add an alt text, etc