My chilli and capsicum young leaves are crinkled and small with short joints, which micronutrient?

Small, crinkled, cupped new leaves with short spacing between leaves and stalled growth in chilli and capsicum most likely points to zinc deficiency, because zinc controls the hormone for stem and leaf expansion, so a shortage gives small distorted new leaves and crowded short internodes. Some crinkling and cupping of new growth can also signal boron shortage, which additionally causes brittle, corky and dead growing points, so the two are worth separating. Because both are immobile and hit new growth, and because crinkled cupped young leaves can also be caused by leaf-curl viruses spread by whitefly or thrips, by mite damage, or by herbicide drift, please do not assume a deficiency from the leaf look alone. Check for tiny pests under the leaves and confirm with a soil or tissue test before treating. If zinc is confirmed, a foliar zinc sulphate spray around 0.5 percent with a little lime, repeated as advised, plus soil zinc at sowing per your card, is the usual correction. If boron is confirmed, a small carefully measured borax application or low-concentration spray is used. Match doses to your soil test and local KVK advice and do not over-apply, boron especially.