In the room temperature thermal energy exits as vibration or long length electromagnetic(EM) waves or molecular kinetic energy, etc..

At the high temperature I suppose EM wave energy ratio may be high.

Then the highest temperature thermal energy is like this.

High UV -----> X ray--------> Gamma ray---->?

And the remained energy is stored as quark-gluon plasma state.

How shortest wave length EM wave is possible in the real physical world?

And the next step?

Is the highest cosmic-ray EM wave? For example 1x10²⁰eV.

Can't electrons vibrate at ever higher relativistic speeds given ever-increasing energy? I would assume that they would thus emit ever-shorter wavelengths of radiation, but maybe there is some limit such as the plank unit of smallest energy-unit?

At the beginning of the Universe, why the high temperature inflation did not make many black hole?

The very high temperature behavior , I think, is not same as low high temperature.