One should not wait to go completely bald before getting a hair transplantation surgery. On the contrary, waiting until you lose all your hair will be a wrong choice because the higher number of grafts transplanted in hair transplantation surgery, the better, the healthier, denser, and more natural your transplanted hair will look.
It is not possible to cover (with transplanted hair) the whole scalp in one session after all. The patient may have to have hair transplantation sessions every six months and continue getting the hair transplant. Therefore, it is best that those who have reached a certain balding level/stage in their hair loss pattern or who have regional/local hair loss have hair transplantation procedure.
If your hair has recently started thinning, and the scalp skin is not visible, only you have a bit of thinning, then it is not a good option to get hair transplantation. You can go for other hair treatments such as hair PRP, hair mesotherapy, and hair shots. If the patient can see balding areas on their scalp when they look in the mirror, if you can see the skin of your scalp, then you might qualify for hair transplantation.