> this scalar field would manifest differently in the equations It shows up in the Einstein Field Equation as part of the stress-energy tensor. That is not a p

> this scalar field would manifest differently in the equations It shows up in the Einstein Field Equation as part of the stress-energy tensor. That is not a problem at all. > and basically be something that enters alongside a cosmological constant. The "cosmological constant" can just as easily be moved to the RHS of the Einstein Field Equation and also considered part of the stress-energy tensor, yes. There is no issue with that at all. > Making dark energy or Λ itself vary Is something nobody has claimed to be doing, as the GP said, so you are attacking a straw man. "Varying dark energy density" does not mean trying to make the cosmological constant vary. It just means adding some other component of stress-energy whose density does not have to be constant, but which still produces accelerated expansion. Anything with pressure less than minus 1/3 of its energy density will do that. A scalar field is the simplest such thing, but not the only possibility. None of this poses the slightest problem for the Einstein Field Equation.