This was a really REALLY difficult time to start a new job. Really difficult. My DH is quite senior where he works but he interviews / trains / supports new starters and interns and has always said he wouldn't like to be doing that in this current situation and has described your exact situation as why.
He's been working in the same Industry for years, knows everyone etc but he has also struggled at home for the fact he can't see and interact face to face with colleagues etc ,all the usual WFH lockdown things.
Are there any plans for people to go back to working in your office environment? Is that something you could look forward to doing?
Is being in flight or fight mode because of stress in your job ok (my line of work is very stressful for very specific reasons and sometimes you just end up in this sort of flight / fight mode and it's just part of the job) or is this something you need to address with your manager? Are there certain things that are stressing you out and do you know what would need to change to make this better for you?
I don't think there would be any shame in going to someone senior with that, as it's a known fact at the moment that starting a job where you can't see colleagues face to face is very stressful and difficult so I think you'd be ok to have that discussion freely if you're comfortable to do so?
Make a list of why it's your dream job (well done! You got your dream job!!) and the good points, things it could lead to in the future and the pros it has over the job you left. Add to the list why you had decided to leave in the first place. Maybe this could help you renew your mindset of why working here is a good thing.
Make some time during the day, every day, to go out and get some fresh air. You say you've cocooned yourself - this isn't healthy. It's good if you're feeling insecure but it's not actually good for you. Go for a walk / go for a swim or gym or something if you enjoy that and there's one local to you.
It's hard to meet new friends in a pandemic, and you would have surely made some at work had you been there in person. When did you move to this city? Are you prepared to make some effort to meet people on an evening perhaps - find and join a book club or a crafting group - plenty of shops that sell yarn and crafty items run local craft groups, if even seen some advertised in my local Hobbycraft. Hear me out but you could look for a WI (women's institute) group. Quite a lot of them are becoming much more modern and have lots of younger members and do some really interesting things so that could be something where you could meet people. If you like spending time with children you could see if you could volunteer with a local brownie / scout etc group and could meet the other adults there.
There's plenty of things out there but it takes some effort and you need to be bold enough to take that step. But for every time you take that step to join something or do something, there will be someone else going there for the same reason, you'll never be alone in that!
I've no idea if this is good or relevant advice for you so I'm sorry if it's not ! Good luck!