Upper limit on the number of humans that can ever exist in the universe (or whatever we evolve into)

Hi folks,

No idea why my brain won’t let this one go. I keep thinking “okay seriously dude who cares”. But i can’t stop thinking about it.

Universe is expanding. Current cosmological horizon is about 16 billion light years i believe? So we can reach roughly 8% of the universe.

There are like 10^23 stars in the observable universe. Assuming each one is habitable, we can maybe spread to 10^23 stars and have billions of people per star system? Say we can sustain this for like a trillion years? 100 years per life, so like 10^42 lives?

Is there any way to get a strict upper limit here based on entropy? Or energy conservation? As in “say we converted the whole reachable universe into humans” or something stupid like that? I know its a silly question, i just wanted to find like a hard “definitely no more humans than X” consistent with the currently understood physics.