The price for power is set by supply and demand. Increased demand for power increases the price. This means that coal plants can afford to operate depending on the amount of demand.
Here’s a story about coal plants closing due to lower demand: https://www.google.com/amp/s/www.wired.com/story/the-covid-1...
Here’s another article about how natural gas plants are replacing coal and nuclear: https://www.mckinsey.com/industries/electric-power-and-natur...
Any increase in demand for power will increase carbon emission by keeping coal plants from shutting down, building more natural natural gas plants, and keeping those plants online more often. Renewables are important, but only satisfy a minority of demand for electricity.
In CO2 free future we'll have all of home heating running on electricity and all of our transportation too. Power generation needs incredible amount of investments over the next 50 years. I believe crypto mining might drive those investments so we are ready for that future.
Even now there are instances where flexible demand of crypto miners helps balance the grid now: https://www.bloomberg.com/news/articles/2020-09-01/bitcoin-m...
But not to drive up demand there are better ways to do that in case of housing. There are places where more efficient housing can't be built bot because lack of demand but local regulations that serve local wealth owners.
Waste food... Not so much bacause food preduction doesn't really suffer as a result of low demand. We pretty much grow food as efficiently as it is possible and in places we don't we do it for different reasons than just lack of demand. There are food producers that destroy some food they produced to drive up the prices by increasing ratio of demand to supply.
Coal power plants close because there are cheaper ways to make electricity now, not because demand dropped.
Crypto mining operations can provide load on-demand which is almost as good as power production on demand while balancing power grid.
Nuclear power plant plus huge crypto mine can provide as much flexibility as coal power plant if not more.