[pluma]

What you're experiencing indeed doesn't sound like burnout. It's plain old alienation. Big corporations are the prime example for this, small startups generally promise to alleviate this (though obviously this only holds true to a degree unless you hold a significant share in the company).

See also: https://en.wikipedia.org/wiki/Marx%27s_theory_of_alienation

At least having worked in Big Tech you have likely built up enough resources to be able to just do something else now, rather than being stuck in this situation until you can retire (or become physically unable to continue working).