> I realized how mediocre and untalented I was
Read Peter Thiel's "Zero to One" and rejoice then. One of the key ideas in the book is that to be successful you have to avoid competition, and build a monopoly on something to the extent you're able. The monopoly will be temporary, but you must have it to avoid race to the bottom which just makes everyone poor and depressed. The monopoly can be a technology, or a brand, or, in the case of a person a set of skills and a track record. In fact it could also be all of the above, but you _must_ have it in order to really succeed.
It is very unlikely that you're talented at nothing. It is very likely that you're fairly talented at 2-3 different things in fact, you might just not know what they are. So if you find those things and get good at them, you'll very likely to be one of the few people in the world who are good at those 3 things at the same time. And unless those three things are "watching Youtube", "shitposting on Twitter" and "scrolling Instagram", this skill stack could be very valuable, and someone would look at you much like you look at others and wonder how it is they themselves are so worthless next to your greatness.
For me the reason of the past 30 years or so, even the smartest people are not uniformly good at everything, and you can easily be better than them at a myriad of things outside their field of expertise. And that's why teams work better than individuals, no matter how talented that individual is.
> Now, I’m an unimportant technical writer composing documents for developers and users.
See, you're good at something others aren't good at. Most engineers can't write docs normal humans can read. Add a few things to the mix, change jobs 2-3 times to establish an upward trajectory, and you'll be unstoppable.
> My talents are shallow and honestly quite useless
Well, deepen them and make them useful then? You must differentiate to succeed, either through the quality of your skills, or through your skill stack, or preferably both at the same time.
> I blame it on the lack of time
Based on what you wrote, I blame your lack of time on excessive use of social media and the internet in general. You know it's true. Give it up, and you'll be able to focus again, have better relationships, better sleep, more confidence, deeper thoughts, more skills.
And for the love of god don't tell other people you're "bipolar schizoaffective". I'm sure it's a real problem for you but others don't want anything in common with that. Paraphrasing a vulgar Russian proverb: "Why would I want a Dick without a dick if there are plenty of Dicks with dicks?" ("Нахуя мне без хуя, когда с хуем до хуя?"). Don't ruin your chances out of the gate if your disease is manageable. And also don't use your disease as an excuse to not succeed. Plenty of people overcame much greater adversities than you'll ever experience.
Above all, if I could leave you with one thought: nobody will respect you until you learn to respect yourself. Do not self-deprecate. Do not use false modesty. If you're good at at least anything (such as technical writing), put it front and center and develop more skills in your skill stack.