Lots of good suggestions on this thread, I think. I have gone through cycles of social anxiety/withdrawal and periods where these seem almost non-existent in my whole life. Like others, I also believe it is due to a combination of inherited traits and own life experiences. I've also experimented with most of the things / cognitive exercises others described earlier, to deal with it.

I don't have much wisdom to add, just maybe a few quite ordinary things, since you are asking how therapy could potentially help. Exposure and using the T as a sort of inspiration/accountability are practical approaches that, I guess, can help if you are able to keep up with it regularly. If you are into figuring out all the details of why you have these tendencies (other than biological), I definitely benefited from lots of honest introspection and tracing back in that area. Some with Ts, but much more with friends who had similar issues - comparing our experiences, finding patterns, even the mere act of discussions provided social engagement in a form that I actually enjoyed (being interested in psychology).

If I had to name one thing that I found most helpful, it is the acknowledgment and reminders that the kind of peer social rejection I experienced in the first ~10 years of my life (~between age 4 and 10), bullying by other kids in childish and totally unreasonable ways, no longer exists. It is far past and there is no way it could ever happen to me again, no reason to fear anything similar, given that it was linked to a certain developmental period and adults do not behave that way. It is simply an impossibility now, no matter what happened a long time ago. Any similar things my mind automatically relates to the current reality are pretty much projections. It's like there is this ever-present low-grade anxiety (which I really believe is simply biochemical), a feeling, and my mind tends to project it into the environment, other people, creating many layers or "threats" that are purely imaginary. It's kinda like a sort of transference reaction.

Other things that are kinda cliche but tend to help me tremendously is good, regular self care. The way this helps is related to what was raised earlier - taking care of myself consistently(!!) alleviates insecurities and self-hatred related to both body and mind very powerfully for me. I can't ever imagine talk therapy having the same effect as it is way too simple and never addresses the many layers of physical discomfort that can underlie a lot of the social anxiety. Addressing and treating those physical things/needs can help me more than any amount of thinking and talking. I had to learn how to do these as an adult as I grew up with parents who were terrible at self-care themselves and thus dismissed my such needs as well - I did not even realize them too much until I was a grown up and experienced issues due to self-neglect. It is still a constant challenge to keep it up but I find if I take care of my physical body appropriately, I have much more confidence and motivation to go out and engage with others.

Finally, I find it helpful to discriminate between simply not having a desire to socialize and attend events at times and actual anxiety/avoidance. It's basically just takes a honest look at my thoughts and feelings, but not always easy, given that projections are often unconscious. I give myself lots of alone time and solo activities because they are essential to my well-being. And when I want private social life, I like to choose the people carefully - I prefer to socialize based on my actual solo interests, not just for the sake of being with other people, most of the time. Find people that are interesting to me - it brings the motivation to spend time with them sort of effortlessly.