The worst method for overcoming social anxiety, but 100% working: poverty.
If there is no money, no food, no car, but you need to eat and move around, then you shove your social anxiety up your ass and go get money. Believe me, I sat at home for several years, trou-hikkikomori and did not communicate with anyone, only a computer monitor and pink ponies, my mother brought food. But when one morning you wake up on the ground, alone, in the forest, thousands of kilometers from home, without food, with 20 cents in your pocket, you have to survive. Anxiety doesn't go away, you just communicate and act through it. Even now I don't communicate with people as soon as I have a little money.
Truth: There is nothing good in life. It's just stupid survival. The worse the conditions, the faster you spin on adrenaline and the less time for suffering. As soon as you get enough resources for a break, you immediately lie down and realize the fucked up situation. It's like walking alone for weeks on a solo trekking in the mountains, sleeping on the ground, swimming in mountain lakes with glaciers, walking all day in pouring snow and rain, wet to the last thread, coming to a mountain lake with a glacier, swimming in it three times a day, and so on every day, and you don't get sick. You go down to the people, go home - there was a slight draft in the car and you immediately came down with a terrible cold.
The human body and brain are not designed for a comfortable, quiet life. Nature is a monster with bloody fangs and claws. Including people. For hundreds of millions of years, all of our evolutionary ancestors lived on the brink of death from hunger, cold and violence (plus infections), where everyone tried to kill each other or cooperate with others to kill. Anxiety in such a world is more than natural.