>I just can't do any of that because I'm extremely introverted
Mate, over the past few days I've written hundreds of words on a nepalese naxalite bulletin board about how talking to women works. Does that sound like something an exrovert would do? For every day I spend practicing this shit I have to spend a day and a half alone to recover. Being 'introverted' is not an excuse. Learning social skills is something that anyone can and everyone should do, regardless of what position they start from or what hindrances they might face. There is practically no ambition, no activity, no dream in this world that can be achieved without somehow engaging other people.
>impacts my social skills and prevents me from developing a real social circle
Don't worry about whether you 'have a social circle', that shit comes after you're comfortable introducing yourelf to new people. Gotta walk before you can run.
>image people have of me as a pathetic loner
Unless you're in high school, if you don't talk to people I can guarantee you that nobody has any image of you at all. Once you start socially engaging with people, they're gonna think you materialised out of thin air in front of them, even if you've been in there for years. If you are in high school don't worry about it, just turn this info into a plan that you can implement as soon as you get to uni. High school is unreasonably difficult on account of how there's nothing to do and everybody's neurologically incapable of empathy. You either luck out early with sports, money, etc, or it's hell. Fortunately there are no consequences going forward.
Your self-loathing comes from a history of social failure, right? You've used the data you have to build a model of yourself and the world. You only have past evidence of failure, so failure is your only possible future. If you want to challenge that model, you need to generate enough contradictory evidence to invlidate the ld model.
What you need to do is start racking up some successes. The trick here is to move at a pace you can manage. If you can't bed a woman, make your goal to have a conversation. If you can't chat, aim to introduce yourself. If you can't introduce yourself, settle for asking her the time. If that's a bridge too far, practice making eye contact as you pass people in the street. If terror consumes you at the very thought of that, do it wearing sunglasses. I don't give a shit who you are or what ails you, you can look at a passing stranger's eyes for 2 seconds while wearing fucking sunglasses.
>how many nigh-impenetrable barriers there are between me and getting something
Social skills are somewhat unique, in that the barriers are only as big as you act like they are. Start thinking you're gonna make it and the barriers will be small enough to step over. Refuse to take that first step and you'll be stuck at the bottom of an infinite well.
>that most people just naturally fall into
Comparing yourself to others: the worst, most pointless waste of time. What, just because someone else did it better, quicker, that means you shouldn't ever get some for yourself? Does Chad give up just because GigaChad could pull twice as many women in half the time? Does GigaChad give up because Charlie Manson could convince women to do more than GigaChad ever could? Did Manson give up because Little Ronnie Hubbard made a mint where Manson only made a life sentence? Did Hubbard give up just because Jesus inspired so much more wealth transfer and slaughter than Hubbard's puny charisma could ever manage? Did Jesus give up just because he'd never be able to escape his weak human side like dear old Dad? Fuck no man, they did it anyway, and they all came away with something. The prizes ran the gauntlet from "Laid" to "The Kingdom of Heaven", but the point is that everyone who didn't start got nothing.
The only person you're in competition with is your past self. "Ha! That autismo cunt would never look anyone in the eye. I did it twice! An infinity percent increase over the best that idiot ever did", etc.
So you can talk eloquently on some subjects, especially ones you've insight on, but clam up at other times. To me that sounds like you don't talk when you're out of your depth. It's a good habit, overall. Nobody likes the arsehole who runs his mouth about shit he doesn't understand. The problem (I'm guessing) is that you end up out of your depth on 'normie' topics. You probably then enter a bit of a spiral, where you think your silence betrays your lack of experience of this normie thing, which marks you out as an autistic impostor, which means they hate you and don't want to hear from you, which deepens your silence, etc.
If what I've described above is the case, there are three things I can suggest:
First, as mentioned upthread - try asking questions. Even if they're idiotically simple. Even if they're just echolalia + uptalk. You interlocutor gets to talk more, you give the appearance that you're interested, and you stand a chance of learning something that you can use to break your silence in a later conversation.
Second, and this'll probably sound weird - take notes. Note down the circumstances that presage your silence. Who are you talking to? What topic was under discussion? Any other pertinent information? Go over your notes - post them here if you want. Find patterns. Outside of the pressure of a social interaction, can you think of anything to say about those topics? If so, memorise it! Then you'll have something to say next time it comes up. Keep that up and you'll pretty quickly have something prepared for most topics that come up (you'll also learn how small is the range of topics covered by most people).
Third, practice changing the subject. Conversations aren't all one way. You're not just there to please the person you're talking to with no regard for yourself. A good conversation meanders around, finding topics that both participants are happily able to talk about. There's no rule saying you have to stick to something you can't speak on. In any case, intervening to change a topic, especially in a group conversation, is a great way to improve your assertiveness. You can take note of and practice the kinds of things that get people to pay attention and comply (volume, tone, gaze, wording, etc).
Honestly mate, you'd probably be best served just taking notes and making plans for what you can do after the rona subsides. Otherwise I'm sure there's all sorts of clubs or hobby-type things that have moved to Zoom and whatnot, that'll at least get or keep you in the habit of interacting with human beings. Your social development wouldn't be advanced by you catching the plague.