[nojster]

The general answer is: through proof of stake.

Since this is HN, you might enjoy this paper: https://arxiv.org/abs/0805.2815 originating from a project called Cardano, which has published dozens of peer reviewed papers (not only on arxiv), presented continuously at EuroCRYPT and works with great academics from “boring” fields (at least to most CS students) such as formal verification.

The main gist in pos (to which Cardano showed the first viable solution that does not have extensive unbonding periods or requires centralized coordination) is that stake pool operators (similar but different to miners in Bitcoin) are chosen randomly to validate the next block based on how much tokens are staked with them. The incentive system to keep these SPOs truthful is outlined in detail in the above mentioned paper.

You basically do not let everyone hunt one complex problem (where all but one miner waste their energy to secure the network) but build a system to chose one to then perform a validation. This decreases energy consumption of the overall network substantially.