My kindergartner refuses to practice writing letters and I'm worried about first grade

My son Mason loves when I read to him and has amazing verbal skills, but absolutely refuses to practice writing... He'll cry, throw the pencil, or just scribble aggressively if I try to work on handwriting with him. His kindergarten teacher says he's behind on fine motor skills and should be practicing at home, but it always ends in a meltdown.

He's starting first grade in the fall and I'm stressed he'll struggle with the increased writing expectations... I bought special pencil grips, tried tracing in sand, even got those dotted line practice books. Nothing works. My mother-in-law thinks I should "force him" to practice daily, but that feels wrong. Has anyone navigated this successfully without creating a child who hates school? I'm worried this is setting him up for failure 😔