Energy in physics feels analogous to money in economics. Is a manmade medium of exchange used for convenience. It is the exchange medium between measureable physical states/things.
Is energy is real in the same way money is? An incredibly useful accounting trick that is used so frequently it feels fundamental, but really it’s just a mathmatical convenience?
Small aside: From this perspective ‘conservatipn of energy’ is a redundant statement. Of course energy must be conserved or else the equations are wrong. The definition of energy is it’s conservation.
It’s as made up as time, but it’s as real as anything can be understood to be, with emphasis on ‘understood’. It doesn’t exist in actuality mostly because our words and models don’t describe it even close to well enough to consider the actual thing. It’s like a really poor translation of a word, it might get us closer to understanding what’s going on but will never be if your goal is to describe it to something like the human mind.
If a one-ton boulder rolls down an Earthly hill in my direction and I don’t move, what happens is not a manmade concept. Call it what you will.
Time on the other hand exists only as a useful mental tool to describe change. When I repeat the experiment of going to sleep, when I wake up it’s still always now. That experiment -always- produces the same result.