You absolutely still need private investment in a growing economy to produce and invent these technologies.
What the government incentives then can do is speed up their rates of adoption and installation. But you need both sides -- public and private.
The whole history the twentieth century is the evidence that such a system doesn't work. And it especially doesn't work as technology has become increasingly complex.
Markets are vastly better-informed investors than governments can ever be. Which is why it's generally vastly better for governments to skew incentives for private investment to favor a particular area, rather than make investments directly.
The government doesn't need the private sector, it allows the private sector to exist where it's deemed beneficial.
The reason this is not a good trend is that the KIND of R&D businesses do vs government are very different. Government invests in basic research and invention while business invests in innovation.
Less money is going into science and more into squeezing money out of people via innovation. I would argue this is because the sector that makes all the important decisions is now the FIRE sector, which only thinks about the next quarter.
source: https://ncses.nsf.gov/data-collections/national-patterns/202...
Even in a stagnant economy, people are still commuting to and from work in their gas-guzzling cars, and heating their homes in the winter. CO2 emissions aren't going to change a ton.
But what a stagnant economy does is prevent any kind of investment in renewable energy and electrification, because there's no excess money to use for investment. A stagnant economy is not installing solar panels, replacing ICE cars with electric and installing new charging stations nationwide, or replacing boilers with heat pumps.
And if we want to hasten the changes to renewable energy and electrification, that's what government policy is for -- via subsidies for desired technologies, heavier taxation for undesired ones, and regulation.
"Crashing the economy" to slow down climate change is like cutting university faculty by half in order to combat grade inflation. It doesn't make any sense.