WordPress 5 changes the way images are added to your content. Images now have their own image block.
To add an image block to a post or page, first create a new block. There are several ways to do this, but the easiest is to put your cursor at the end of a paragraph block and then press the Return key.
After you publish your page, remember to view it on a mobile device. Note that if you’ve aligned an image to the left or right of a paragraph, you may have to adjust its size so that it fits properly on the smaller screen.