There are several confounding factors so it’s hard to know for sure, but I do think that Toastmasters has helped me improve at a specific sort of social interaction: having to talk when I don’t know a lot about a particular topic or when my thoughts aren’t well prepared. I’ve gotten a lot of practice at this with an exercise Toastmasters calls “Table Topics”. During Table Topics, each person goes up to the front, is given a prompt, and then gives a 1-2 minute impromptu speech on the given topic. Table topics force you to talk for at least one minute about topics you sometimes have no interest in or think you know nothing about, which has helped me develop some useful skills:
I usually know more about things than I think I do, and quickly accessing this buried information is something I’ve gotten better at. I think I know almost nothing about football, but if I actually take some time to think about it, that’s not true. I have a vague understanding of the rules, and know about brackets and betting, and know some things about head injuries. I can talk about these things.
I’ve gotten much better at taking a topic I’ve been given and transitioning to a related but more comfortable subject. I might be uncomfortable talking about the Superbowl for a minute, but I could transition to instead talking about other athletic competitions I know a lot about, like marathons and ultramarathons.
In non-Toastmasters settings, these skills have been useful when I’m trying to talk to people who have different interests, or when I’m put on the spot to talk about something I feel like I don’t know a lot about.
For example, if you have a "shy person" identity, then going to parties or starting conversations with strangers can generate counterexamples for that identity, and help to displace it with a new one of "sociable person". Costly signaling can be used to achieve this - for example, joining a public speaking club.
Counterintuitively, I think that joining Toastmasters has actually made me identify more strongly as an introvert, mostly because my introversion is never more painfully obvious than when I'm there. So, observing myself attending Toastmasters isn't enough for the "sociable person" identity to stick; I'll have to get to the point where I observe myself attending Toastmasters and also observe myself not feeling terrible about the whole talking thing while I'm there.
That is a useful reframing. I’ll give it a try!