I think your therapist is onto something, and honestly after nearly 3 decades running into burning buildings, I've seen enough to know this matters. When you're facing real danger or loss, the stuff that keeps people going isn't always logical - it's the meaning they've attached to things. A firefighter runs into a fire because of what that job means to them. A parent goes through hell for their kid because of what that relationship means. The "invention" part doesn't make it fake any more than a wedding ring is fake just because humans invented the concept of marriage.
Here's the thing though - meaning isn't like a lie you tell yourself to feel better, even if you're technically constructing it. Your brain actually *needs* narrative structure to function. It needs to know why it's doing things, what matters, what the goals are. Without that framework, people fall apart. Depression, anxiety, burnout - a lot of that comes from not having coherent meaning, not from the meaning being "invented." I've seen people thrive on meaning that sounds totally made up to someone else, and that's fine. It works for them.
The real question isn't whether meaning is objectively real or fake - it's whether it's *yours* and whether it actually guides you toward the life you want to live. If you believe your work matters, that your relationships matter, that your effort means something, that belief changes how you show up every single day. After 28 years and thousands of early mornings, I can tell you that mindset shapes everything. So does it matter if it's "invented"? Not really. What matters is whether it helps you live better.