[orzig]

Totally agree on the importance of feedback - another idea (a little expensive, but I'm assuming the OP has resources) is a coach/therapist/etc. Doesn't even need to be social-skills-focused. Anyone in that work obviously has above average social skills, and they want to help you. If you make it clear that it's a priority, and ask some specific questions like literally "Could I do anything to smell better?" to "Is my haircut/resting face/T-shirt off-putting?" they will do their best to gently guide you.

Even a trainer at the gym could probably do it, which might feel more comfortable and probably easier to schedule. A little exercise never hurts, and the gym is a great way to just be around people and practice all sorts of brief interactions. You probably won't find your best friend there, but that's exactly what makes it low-stakes and a great place to start.

[orzig]

Another "first step" place to practice social skills is in the Open Source Software community. It sounds like you (OP) are familiar with the technical part of coding broadly defined, so it's an opportunity to be 80% in your comfort zone while experimenting with a bunch of human interaction. I'm reminded of this because HN's front page currently has a nice guide to interacting in the OSS community: https://polite.technology/preview

You'll want to eventually graduate to things like body language, but if you get a little lucky you might be able to build some comfort with people through e.g. Github and then take another step into video chats and, if you're really lucky, in person someday. Even if the 'in person' people end up being different OSS people than you worked with digitally.