Renewables are one option for massive investments without massive long term costs. The important thing is to subsidize them upfront rather than subsidizing their income stream or you get high electricity prices.

However, the idea of stimulus makes basic assumptions that the economy can sustain a higher level. That economic article of faith may inherently be flawed in many cases.

Another option for developed countries is rather than trying to stimulate the economy instead focus on increasing efficiency. Japan’s workforce increased 1% in the last 22 years. Long term stagnation should be expected in countries like Japan with stagnant and aging populations. Even 1% growth assumes the economy will double every 70 years. Relative stagnation isn’t inherently bad as long as the economy is still doing all the things an economy should be doing.