Now, for someone who is not in this particular bodily (and mental) state, life itself is a joy. The concept of meaning of life doesn't even come into question, because if you love waking up in the morning, love the work you're doing, the people you interact with and society and the world itself, you don't feel like you're lacking anything. There is no need for further meaning.
Also, this state, like all other bodily functions, is not a discrete, binary switch, but a continuous biological mechanism that takes a spectrum of values. It can be measured by simple tools such as the activation of the vagus nerve, brain activation pattern revealed on an EEG and so forth.
As for how to change this bodily function, unfortunately that is still a bit of a mystery. Some find that seeing a therapist helps, changing of your personal circumstances often helps as well. There are other promising mechanisms such as neurofeedback, but none of them have a perfect track record.
The fact that life is inherently meaningless means that you're not doing it wrong, rather, that you can't do it wrong, and is therefore more free to explore and do what makes you happy.
Just imagine how sucky it'd be if the meaning of life was to carve this giant figure in a mountain, but you'd much rather go swimming..
I have a small fear that life turns out NOT to be meaningless, because if that was to be the case, humanity is wasting time not doing what it was meant to do, and we should have a meeting (all of us, on the planet), coordinate and work towards the correct goal, and, oh damn.. that'd be really hard work.
In the `80s I realized that watching the evening News left me feeling depressed. I was being barraged with news about violence, murders, rapes and robberies, deadly accidents (autos, planes, trains, etc), wars, racial strife, poverty, disease.
It finally hit me one day when the "News" wrapped up with graphic video of a deadly car accident somewhere in Africa. I realized that when I got up that morning I felt fine, but after watching the "News", which began with local news (I was living in Los Angeles), then National News, then World News, I felt as though the entire planet was filled with awfulness.
After sitting there pondering that I realized that in my own personal life things were not near so awful and that led to the epiphany that I needed to focus on that instead, and to do that I had to stop taking on the weight of the entire planet's terrific events. I had to put that in perspective.
The "News" channel I was watching was an independent TV channel that became one of first to be purchased by Rupert Murdoch to form the "FOX" network. Tuning out provided immediate relief. But I didn't tune out just them, I pretty much stopped watching TV "News" altogether.
That was "Step 1". The next step was to begin focusing on things I enjoyed. I could list some of those here but this is something we all must figure out for ourselves.
I can watch the News now and maintain a much better perspective of how it affects me personally. and for the most part it doesn't.
Right now, today, people all around me are stressing out about what's going on in Washington DC. I am not. I cast my votes last year. My 1st choice lost. I'll deal with what comes as it comes but I will not fret about what may or may not come. I'll enjoy what I can instead.
I believe if there is a "meaning" to it, it's to learn how to appreciate it. If you can do that living becomes amazing.
The answer is going to be a lengthy dialogue that's personal to you, but I'll give you a bit of a shortcut pointer: you're unhappy, and you want to be told a route that will make you happy in some long term. Acknowledge the unhappiness, and start to work on yourself.
Ideally you'd do that with a professional therapist, if possible, though finding the right therapist is a challenging task in itself. They're not there to give you answers, but to help you frame the question and encourage you to think seriously about it. It's easy to think you have, but instead just wear ruts in your existing thinking patterns.
So I've hopefully given you a new way to think about the question. Start there. Forget about "meaning"; it's a red herring. Ask yourself why you think that red herring is important, and maybe by looking sideways at the question you'll find some answers that are useful. Good luck.
(This is what you do if you get diagnosed with terminal illness btw: you get your affairs in order, you gather your loved ones and you try to make the best of your limited time left, and it'll be good enough)
Maybe we just did not find it yet? It's not inside the knowledge we have, so it might be beyond it. To find it, we may need to expand our knowledge about the world, i.e., do science. This is how science may (temporarily) replace the meaning of life.
And you don't have to be a scientist yourself. Instead you may help it in any way you like: spreading knowledge in humanity, preventing conflicts, providing necessary services, etc.
But maybe you don't agree with that. Maybe you think that's just a fantasy, a nice game of pretend that I play to keep the meaninglessness at bay. Even so, I think that our human nature is to need to love and be loved. If God isn't there, well, people are. Love them. Be loved by them.
Being responsible to provide for them is meaningful.
Friendships can be meaningful.
Works for me.