A wound closing and a wound finishing are two different events. Closure is the part you can see. What follows it is not visible, and it takes considerably longer.
StatPearls, a clinical reference available through NCBI Bookshelf, describes the final stage of healing as the maturational or remodelling phase. It starts around week three and can last up to twelve months. During it, wound contraction peaks and excess collagen is broken down as the repair is reorganised.
For surgical incisions specifically, the same reference puts maximal tensile strength at about eleven to fourteen weeks. Tensile strength is a measure of how much force the repaired tissue can take, not a measure of whether the wound has closed.
It also makes a point that matters more than any single figure: the resulting scar never has one hundred per cent of the original strength, and reaches only about eighty per cent of the tensile strength of the tissue it replaced. Repaired skin does not become identical to the skin it replaced.
The European Wound Management Association puts the same idea in plainer terms in its patient Q&A: a wound may be closed on the outside while it takes months before the inside is completely healed.
What none of these sources give is a date. There is no week at which skin stops being fragile and becomes ordinary again. What they describe is a gradual process with a long tail, not a switch that flips.