The verb knit is traditionally uninflected in the past tense and as a past participle. Knitted is now well accepted, though; it appears about as often as the uninflected form in 21st-century texts from throughout the English-speaking world.
Knitted is safest as a participial adjective (e.g., a knitted scarf), but it also works as a verb (e.g., she knitted all morning). Knit also works in these uses (e.g., a knit scarf, she knit all morning), but it’s falling out of favor.
A chunky knit scarf coils around his neck like a python and then trails down his back … [Truckee Times]
She knit and crocheted some baby items and childrens hats and scarves for our American Legion Aux. [Village Soup]
Packer has knit the scenes together intelligently. [Boston Globe]
The compulsory purchases include a knitted hat and a waterproof jacket bearing the school logo. [Guardian]
He knitted the trail clubs together into a cohesive group. [Baltimore Sun]
Others have knitted sweaters with a working QR code stitched in. [Los Angeles Times]