Comment on "Measurability of nonequilibrium thermodynamics in terms of the Hamiltonian of mean force".

In a recent paper [Phys. Rev. E 101, 050101(R) (2020)PREHBM2470-004510.1103/PhysRevE.101.050101] an attempt is presented to formulate the nonequilibrium thermodynamics of an open system in terms of the Hamiltonian of mean force. The purpose of the present comment is to clarify severe restrictions of this approach and to stress that recently noted ambiguities [Phys. Rev. E 94, 022143 (2016)PREHBM2470-004510.1103/PhysRevE.94.022143] of fluctuating thermodynamic potentials cannot be removed in the suggested way.