I am scared of my future. Need a genuine answer. I couldn’t see any software engineer whose age is > 40 What do they do after 40?

They are sent to a farm upstate where they live happily forever.

Move to managerial career, or start their consulting arm

And I have seen many 40+ aged software engineers. You might be working in Service Based companies. In product based companies, you can easily notice 40+ aged software engineers- usually at Principal Engineer, or at Architect roles.

the rich ones move to smaller cities/town if their kids are all grown up. people who cannot move out, become freelancers.