Your earlier post that you reference says “Enthalpy of a system is essentially a measure of how much energy it takes to create the system from nothing”. The energy you are describing is E=mc^2 not U + PV. However, according to my textbook enthalpy is defined from the point of view of the system. If the system creates the space needed for its existence (as you imply) then it would lose energy and PV would be negative, not positive as when PV is added to the positive kinetic energy. So this doesn’t explain why enthalpy seems to involve conflicting definitions of the sign of PV, nor why PV is relevant if P is constant.
Your reference repeats the idea that ideal gas molecules don’t interact (rather than involving the approximations that their volume is negligible and their interactions are simple elastic collisions). If gasses at different average temperatures are allowed to mix, how does their kinetic energy tend toward Boltzmann’s distribution if they can’t interact? In what sense is it ideal to defy Boltzmann’s equation?
Implying that I’m confused about some of the traditional ideas that you and others keep repeating isn’t helpful. Adding more such ideas doesn’t help either. I’m seeking logical explanations, not repetitions that ignore the points I'm making about the repetitions.