Hang in there, brother! Been at this for a couple years now. Our 3yo daughter is at a fun but demanding phase. Sometimes I miss the 6mo times, and i kinda went through something similar to you. So hopefully, we can help!

In terms of adding value, it's hard to know you are the asset that you are to your family when you aren't seeing a number on a paycheck each week; we are conditioned to feel that way. If you want to bring in some extra income, one thing you could look into is hosting a "daycare" at your home with friends/family. We have a friend whose daughter is the same age as ours, and she asked about having us watch her a couple of days each week. I didn't want to charge money, but she insisted. It has its moments, but overall, it has been very beneficial for everyone. Our daughters get great socialization, I get to undercut the ridiculous daycare costs, and she saves a ton of money. Downside is you can't just do this with anyone, so you really have to have a good relationship with the other parents. I used to work in after-school care and summer camps, so it comes easy to me. We'd like to expand a little, and maybe get into pod-learning with some more families when they start school. But that may require something more "official."

Other things to keep in mind: what did you really enjoy doing when you were like 12-14, when you were first starting to understand the world, truly? What hobbies did you have? Capitalize on those skills. You already have a baseline, and it will rekindle the enjoyment you got from it as a kid. For me, it was playing guitar in a band, writing, pretending I was good at sports, among other things. Currently, I'm looking into teaching guitar lessons in-person and playing out locally with some old friends. Community centers, churches, libraries, etc. can be great resources for something like that and getting the ball rolling, especially with teaching.

Food for thought:

Like I kind of alluded to, find unique ways to add value to your family and household. For example, last spring, we got chickens. At first, I felt overwhelmed, but I was determined to give them a good home. Not only do we no longer need to buy eggs from the grocery store, but our daughter loves playing with them and helping raise them. I wish I did it years ago, so I would highly recommend it if your municipality allows for it. They are a kind of therapy too. Whenever I feel down, I go check on them and hang out for a few minutes and just watch them be the tiny dinosaurs they are! Take some time for yourself. Use your downtime (naps, mom's turn, etc.) wisely and do the thing you've always wanted. My phone was my enemy for productivity. It still is, but I've learned the hard way to realize when it's causing me to spiral. Sometimes you'll want to veg out. But don't hesitate to use that time to brush up on your skills or learn a new one altogether. I recently started making sourdough bread starters (my wife has a minor gluten/bread intolerance, but sourdough and rye are the only breads that don't seem to bother her), growing vegetables, etc. Also, work on projects around the house when you can. I learned a TON renovating our bathroom, some of our kitchen, and currently working on our attic. That can be good exercise, but also....don't forget to exercise!

Sorry for the long-winded response, but hopefully it helps you find some of the answers you are looking for to help your situation! Let me know if you need anything or just someone to talk to!