Here's another creative tip for written output struggles.
Use post-it notes or stick notes to tell a story. It works very well if you have all kinds of different sized and shaped and coloured Post-its. Begin big using a large piece of card. There are sooo many ways to do this, but a few I've found especially helpful are both you and the child write single words and then together build some silly sentences to warm up.
You can then proceed to an actual story. Sticky notes because of their size limit the amount of words and it's much more manageable for the child to tackle writing on that smaller space than a big blank page. You add the notes side by side to form the story. Take breaks to reread what the child has created and that should create impetus to continue. The tactile aspect of manipulating the post it notes really makes it fun for the child.
If you can find sticky notes/post-its which are in the shape of speech bubbles you can use them on pictures to illustrate speech. They can also be very fun to write a story and then every time someone speaks use a speech bubble for the words. The story will look fun and the child should get caught up in noticing when the next speech bubble is needed.
If you can find them shaped like flowers or animals you can place a single one in the middle of a page and build a story with small square ones around the shape in the middle. So a story about a flower or a ladybird. You can also cut out regular yellow square ones into particular shapes and build stories from there.
These ideas work very well as "guessing games" where you're building stories together and the child has no idea what's coming next. Humour is a great tool, so add humorous twists to the stories to keep the child interested.