One of the most effective ways of reducing power usage of software would be to prohibit proof of work, and get rid of it. For the fucking love of god, and to save the planet, fix Bitcoin.
The second most effective way to reduce power consumption of software is to get rid of generative AI (GenAI), specifically training (inference is largely harmless).
And in fact everything else does not matter **AT ALL** in the grand picture, and is an utter waste of time.