Okay, so let's cover a bit of ground here first.
Let's talk depression vs suffering.
Depression and suffering can manifest the exact same way: feeling hopeless, inability to enjoy things, inability to feel at peace with life, etc, etc.
The major difference is that suffering is a normal, reasonable, and proportional response to a negative event in your life. It can be even more severe than clinical depression. For example, if someone loses a child, that can result in a totally proportional level of suffering that is totally unmanageable and unbearable.
But it's NOT depression.
Life events can't cause depression, but they can trigger it. So mourning can trigger a depression and that person then doesn't recover from the mourning on a normal timeline.
Depression is an *abnormal* state of suffering that is not or no longer reasonable or proportional to the events happening in the person's life.
Both can require similar treatment, but the distinction is VERY important, because the treatment is meaningfully different.
For suffering, the treatment can require medication, but is primarily about processing the traumatic/negative experiences to make sure that they don't create maladaptive patterns of thoughts and behaviours. When someone experiences something difficult, a loss, a major change, abuse, etc, it can either entrench itself and make the person overall less healthy, or it can be processed effectively and make the person more resilient.
The purpose of treatment is to get the person back to a health state where they can return to their normal, healthy function in life.
Depression is a totally different creature. Depression makes it impossible to be healthy. It's not just a matter of processing things, the brain will simply not allow the person to be able to enjoy their life because they're not capable of a proportionate, normal response to things.
Happy feelings don't last as long as they should, safety never totally feels safe, life just lacks that feeling of being okay.
Now to OP, do you have a proportionate suffering response to major life changes or has it evolved into a mild depression? It's impossible for an internet stranger to say, but as someone with A LOT of knowledge on suffering, I have a strong suspicion it could be that you've had mild depression triggered.
There's nothing actually wrong with your life and you are struggling to find activities and things to *make* your life feel okay. To me, it doesn't sound like that's working or that it's going to work. I don't know that you can solve this problem with "logic" if there's a fundamental basis for you not feeling comfortable and happy in your life.
Let me illustrate with a counter example so you can see what I mean.
I'm in my late 30s, I studied for over a decade for my dream job, I LOVED my dream job, but then got extremely ill, diagnosed with a rare, very disabling disease, and had to give up my dream job, that I LOVED, after only working for 7 years.
I suffered immensely with severe mourning, loss of identity, loss of function, loss of my ability to walk comfortably, and I am in constant, and I mean *constant* pain. I, like you, struggle constantly with figuring out what to do with myself because I physically can't do most things, not consistently. So my life is very limited in many ways.
So I have all of the reasons in the world to be dissatisfied with my life, and yet, I'm quite happy, peaceful, and very at ease with my life. I have rough days, but for the most part, I'm very satisfied.
I didn't always feel this way, I've gone through a lot of therapy to make sure that my suffering was processed and didn't turn into negativity and toxicity. This also helped prevent it triggering depression, which runs in my family.
The only way for me to really accurately describe my current mental health state despite still experiencing a significant, legitimate amount of profound suffering is that I'm *not depressed*. I don't have a better way to explain it other than that I feel like every negative feeling I have is entirely within reason, totally manageable, and doesn't define my state of being.
I'm explaining my experience to help you put yours in perspective. If you feel about your life like I do, that no matter what is going on, no matter how painful things get, that you are still good, and life is still rich and fulfilling, then you're doing fine and don't need any therapy.
However, it doesn't sound that way, and what's critical is to determine if your negative feelings are entirely in line with their triggers, or if you've been knocked into some degree of depression where you literally can't feel comfortable in your life until you resolve it.
Whatever the case, hobbies, a job, etc, aren't going to solve the problem. Not having a source of purpose doesn't make people feel the way you are feeling, there has to be something maladaptive happening at the same time.
As other people have said, that's not unusual for this stage of life. Many people experience difficulties with mental health during this stage of transition in life. It's common, but that doesn't mean it should be brushed off as normal.
Whatever is going on, there is some degree of a mentally unhealthy process happening, and that needs to be effectively addressed, and not by going back to work or volunteering more.
It's time to stop looking outwards for the answers and start looking inwards.
Your life could be much, much worse and if you were perfectly mentally healthy, you would feel better. So tackle the mental health first, *then* focus on figuring out what your best life looks like at this stage.