Hi, i know exactly what you're going through OP. I had the same. It's physically and emotionally draining, for both the parents as well as the child. For us it finally got better this academic year. My DS just turned 7 and thankfully we've managed to navigate our way out of what was causing the meltdowns.
Throughout nursery he was such a happy little boy and really enjoyed going. At 3 and 1/2 he moved to the pre-reception year at a pre-prep school and continued to thrive. Teacher thought he was settled and enjoyed all the activities but noticed he was never really interested in drawing and colouring. I also noticed he was never into arts and crafts at home so we just put it down to it not being his 'thing'. He was doing well with maths and phonics and blending but had terrible pencil grip and hand control.
In the following year he started reception where the school day was more structured and written work had ramped up (he was 4 and 1/2 at this point). During this academic year he struggled with producing written work (short sentences) and while he managed it in class with a little bit of extra time, he would come home and have the biggest meltdowns and mood swings, lashing out physically at me and saying he doesn't ever want to go to school. It used to take up to an hour for him to calm down from his moods. He never behaved like this in school but at home he was uncontrollable. The teacher would always mention he was behind in completing written tasks and was easily distracted in class, he was also very slow in getting changed for PE. but he never had these outbursts.
For the entire year there was a guaranteed meltdown every morning whilst getting ready for school and then every evening another. I was at my wits end until I slowly put all the pieces together and suspected dyspraxia/DCD. I got him assessed privately by an OT and they confirmed delays in balance and coordination, low muscle tone in arms and hyper mobility in hands/fingers which was seriously hampering his ability to produce written work.
The meltdowns/outburst were due to fatigue and frustration. He had to concentrate hard to control hand movement to get words onto paper that he was utterly exhausted by the time he got home. He'd wake up the next day absolutely dreading having to go to school.
Once we understood what was going on we started weekly OT sessions to help him develop his gross and fine motor skills and generally learn coping strategies. Once the school was informed he was supported by the school SENCO and his teacher allowed him extra time to get things done and had a bit more understanding of his needs and let him work at his own pace.
Later on I also started noticing he'd stalled in his reading ability which then prompted further assessments for dyslexia but it turned out to be to do with his eyes not tracking and converging efficiently which added yet another layer of complexity to his experience of learning and school.
Only when we got to the bottom of all this by the end of reception year and put all the necessary support in place did we start to see a dramatic change in his attitude towards school and learning. Year 1 was tough but the meltdowns had almost disappeared (less of an uncontrollable outburst and just the odd request occasionally if he could stay at home, which I would always diffuse by reminding him of all the positive things he enjoys at school, seeing his friends, playtime, golden time, rewards for weekly achievements...).
He's like a completely different boy now and the school has been great with supporting his needs. He still dislikes writing but absolutely loves everything else, including PE which he used to hate because he couldn't do the things the other children could.
I would suggest having a chat to the school senco and also see if you can get a referral to an educational psychologist.