In our universe, in order for a cloud of gas to collapse into a star it needs to release heat energy in the form of radiation, so that it can cool down enough to collapse into a star.
I read what Greg Egan said about the Riemannian Universe on his website https://www.gregegan.net/ORTHOGONAL/ORTHOGONAL.html and also read the Orthogonal series. Both discuss how the main difference between the Riemannian Universe and our universe is that there are four fundamentally similar dimensions instead of three space like dimensions and one time like dimension, and the minus sign in the equation for the spacetime interval is replaced by a plus sign.
In the Riemannian Universe photons would have rest mass and releasing photons would cause a body to heat up instead of cool down because kinetic energy is opposite of total energy, and releasing photons would lower the total energy of an object, and so increase the kinetic energy energy of the particles making up that object. I don't remember either the website or the book going into detail on how star formation would work in the Riemannian Universe and having a cloud of gas radiate away energy wouldn't work for getting it to collapse into a star as radiating would cause the gas to get hotter.
How might star formation work in the Universe described in the Orthogonal Series? Also what might cause stars to shine in this type of universe?