Dark energy is different from ordinary energy if it exists. It’s a property of space itself, and it's not conserved.

I’m no expert on this but quoting from Sabine Hossenfelder (theoretical physicis and expert in such things) then for instance, if you take it as the cosmological constant version of dark energy.:

"According to Noether’s theorem there’s a conserved quantity for every (continuous) symmetry. A flat space-time is the same at every place and at every moment of time. We say it has a translational invariance in space and time. These are symmetries, and they come with conserved quantities: Translational invariance of space conserves momentum, translational invariance in time conserves energy.

"In a curved space-time generically neither symmetry is fulfilled, hence neither energy nor momentum are conserved. So, if you take the vacuum energy density and you integrate it over some volume to get an energy, then the total energy grows with the volume indeed. It’s just not conserved. How strange! But that makes perfect sense: It’s not conserved because space expands and hence we have no invariance in time. Consequently, there’s no conserved quantity for invariance in time. "

Dear Dr B: Where does dark energy come from and what’s it made of?

Other ideas here:

What Is Dark Energy?