I read this thread in the middle of the night. I think a lot of people have felt 'off' since Covid, I know that doesn't apply to everyone, but it does seem a low level depression or lack of optimism has settled over the population. I've seen it with my friends, although each of us seems to be dragging ourselves out recently, and starting to enjoy life again.
If you have the time/energy, read '4000 weeks: Time Management for Mortals' by Oliver Burkeman. He starts from the premise that you are going to die and that you have to work backwards. Doing achievements (like marrying, having children, success at work) rarely bring happiness otherwise the rich married people with kids would all be deliriously happy and they are not. So, what then? He has some suggestions.
Second, I've been trying to think of myself lately as living an 'Ordinary Extraordinary' life. Like most people, I don't 'matter' in the grand scheme of things. So where can I matter? What I hear on this thread is that many people feel helpless and like nothing they do counts. That's a reflection of our society devaluing living a good and ordinary life. I've been working on attending events, ringing a friend, doing a good job at work not because they will make me happy but because they are putting just a tiny sliver of 'good' back into the world. Pick up a bit of rubbish outside my house; work on a project for charity that appeals to me personally. It might be ignored, or even worse, you meet a horrid person and they stick the middle finger up at you when you are driving or whatever. Putting horrible things into the world is essentially a bad thing to do (like when people post mean things on Mumsnet, what have they contributed really, that day?) I don't mean going around being nice, that sounds awful, I mean more seeing that my very minor contributions- even cleaning so my kids have a clean house, or watering my plants on my front doorstep, or chatting to someone, or texting a friend without expecting a reply, isn't adding to the sum of human misery, and that's a good thing I can do in my limited little tiny nugget of the world.
I probably haven't explained it very well, but I noticed on Mumsnet a lot of posts like 'I'm bored' 'I'm unfulfilled' 'I don't like going out with my friends, rather stay home' 'I hate life'- I think asking ourselves to be happy is probably too much. Unless we are going to jump off the world, though, we have to find a way to live through it. Understanding we are both irrelevant and random, but also quite powerful in our own little lives has helped me a lot (if you want to see what happens when people live horrid lives and don't care, clean, or nurture their children, see the stats on what happens to those children when they grow up).
Finally, and this might just apply to me, I didn't notice I'd slipped into a proper depression for quite a while. I definitely shifted from not enjoying things, to actively disliking life, to definitely not wanting to keep living- I've taken antidepressants for the first time in my life and they've been very effective in restarting my interest in living my ordinary extraordinary life!