1
You need to have a property for each value to make just one editable. I've updated your sample code.
array = [];
connectedCallback(){
this.array = [...Array(10).keys()].map(key => ({ key, readOnly: true, value: null }))
}
toggleDueDate(e){
this.array[e.target.dataset.index].readOnly = false
this.array = [...this.array]
}
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