Why does an indoor jasmine plant turn massively yellow and black and drop leaves severely not long after being kept indoors?

A netizen asked: an indoor jasmine kept for not long has turned massively yellow and black, and is dropping leaves severely - what is going on?
Key point: this jasmine of the netizen's is already in great danger; the new buds of the jasmine have turned black and shrunk back, the branches have turned yellow and are dropping leaves. If you want to save it, just cut it back hard and then change the soil and repot it - that is the most direct way.
Let us look at the pictures provided by the netizen:
From this picture it can be seen:
Circle 1 position: the potting soil is wet and severely compacted, which shows the netizen watered too much. If you water too much, the roots lack oxygen, breathing is weakened, and the leaf tips turn yellow and wither.
At Circle 2 position you can see a large number of fallen leaves inside the flower pot; it can be seen that the leaf drop has been going on for some time, which is why the branches look bare and leafless.
At Circle 3 position you can see the branches have almost no side branches; the leaves and branches of the few side branches that can be seen have already turned yellow and look lifeless. The tops of these branches all have holes, which shows the withering is severe.
At Circle 4 position you can see the new buds on the branches have withered; it should have been pruned, but it was no use, the withering and yellow leaves are still continuing, the leaves are withering and turning black - this is the most common situation caused by watering.
At Circle 5 position the terminal buds have shrunk back, caused by too much watering. You can also see it is kept indoors; with indoor keeping, ventilation is poor, which is also the reason the water cannot dissipate quickly after watering, causing the root activity to get worse and worse.
Let us look at the second picture:
From this picture it can be seen:
At Circle 1 position the tops of the branches have already been pruned off, but it seems to have little effect; the withered and shrunk-back terminal buds are still continuing, which shows it is already very serious and the roots should already have turned yellow.
At Circle 2 position you can see there are new branches and new buds, but the new buds and leaves look yellow, the leaf veins are normal, and there are black spots on the tips of the new leaves - this is caused by too much watering.
At Circle 3 position you can see the leaves are withering, turning yellow and black; these leaves are also leaves that are about to fall, the branches are thin and weak, clearly poor nutrition and poor root activity caused by too much watering.
Let us look at the third picture:
From this picture it can be seen:
At Circle 1 position you can see the top leaves are withering and shrinking back, a typical situation caused by weakened root breathing, that is, too much watering.
At Circle 2 position the leaves are severely blackened and about to fall, also caused by too poor environmental ventilation.
At Circle 3 position you can see the new buds that have emerged have already turned black and shrunk back, typical of too much watering.
Through the analysis, the netizen's jasmine problem is mainly caused by too much watering and too poor environmental ventilation, which caused the roots to turn yellow and breathing to weaken, and then caused the new buds to turn black and shrink back and the leaves to wither, turn yellow and black and fall.
The city landscaping gardener suggests the netizen do this:
1. Take it out of the pot, wash the roots and prune
It is suggested to strengthen the pruning; do not be reluctant. For those dried-up branches at the lower position, also prune them; as long as a branch has no vitality, prune it right off, and the other branches should also be pruned. For me, I suggest directly taking it out of the pot and pruning, then washing the roots and pruning, cutting off all the useless roots, blackened roots and some useless branches.
2. Disinfect
After pruning and washing the roots, it is suggested to soak them in carbendazim; the potting soil should also be disinfected.
3. Change the soil
It is suggested to change the soil again; seeing that the potting soil is severely compacted and both water permeability and air permeability are poor, it is suggested to sun-dry the soil taken out of the pot, then mix in some coarse sand grains to increase water permeability and air permeability, because compacted potting soil is bad for root expansion.
4. Pot up in moist soil and keep it in a recovery state
After potting up, put it in a cool, ventilated place to recover. We suggest potting up with moist soil; moist soil lets the roots make good contact with the potting soil, and you do not need to water thoroughly to settle the roots, which avoids infection of root wounds by pathogens. Wait until the potting soil is dry and then water thoroughly once; keeping it this way is better.
5. Absolutely remember fertilizing
After potting up, absolutely remember fertilizing, because the roots have not yet adapted to the pot, and fertilizing easily burns the roots and burns the seedling.