Welcome, NT!
We also have a child who found it very challenging to display cognition and academic achievement through written work at this age. At the time, we were homeschooling, so I simply scribed all of the work except for handwriting itself, and worked on physical writing through short, focused activities (less than 20 minutes a day). As soon as speech to text software was reasonably accurate (at the time, it was not always able to pick up children's voices as easily), we switched to STT for written expression, and continued to scribe or assess orally in other content areas (e.g., math, science, history). Once we had enough manuscript and cursive skill to meet my minimum expectations (write a two-sentence thank you note, fill a form, sign your name), we transitioned to typing instead of handwriting.
For your child, much depends on whether and how he is developing as a whole person. It sounds like many aspects of development are currently satisfactory, but not writing. Are other areas also concerns? He is happy at school, which is the most critical, but possibly not learning much academically, and being given misleading messaging regarding his academic potential especially in writing. Be particularly alert to any negative self-perceptions he might be absorbing from his school experience. Afterschooling or enrichment can be sufficient to maintain a child for a little while if it addresses the areas of greatest intellectual thirst. What does he thrive in?
Secondly, the question of any unaddressed second exceptionalities should not be overlooked. Whether the school acknowledges either intellectual giftedness or dyspraxia, he will--as you've noted--increasingly be aware of them, and it would be best to stay ahead of the narrative for his sake, lest he internalize his challenge areas as the ceiling of his ability. If and when a dyspraxia diagnosis is offered, pay close attention to any recommendations emerging, and ask thoughtful questions about remediation both through professional therapies and supportive home activities. The earlier his challenges are addressed, the less they are likely to impact his access to his strengths over the long term. Our family practice has always been transparency with our children, especially when it is about themselves. Consider how you and your team can most effectively explain to your child what the nature of his learning profile is, and how his diverse abilities affect his daily experience. It is almost certain that he already has some sense that he learns differently from others (on either tail of the bell curve); this will simply give a name to it.
