These guidelines change dynamically and it’s better to contact a travel operator to ascertain this, mostly Negative Report is not required for fully vaccinated travellers in most of the places but not sure of Ladakh. These state-wise guidelines are also available on websites of airlines.
Best time to visit Ladakh is in summer April to July. Summers are warm though not scorching where you get better views of a spot. As far as travel rules, you need to carry your Vaccine certificate. Travel to Ladakh is open. Before planning and booking kindly check the rules and restrictions once again. Happy safe travel.