If "degrowth" is the answer to the question of what the economies in fairly rich countries should do in the near future, then we are asking the wrong question. We need to take a much more nuanced view about what sustainable development (not sustainable growth) should imply for the economy in both the near term and the longer term. Thus, if "degrowth" means that the GDP should go down over the next few decades, then we need to take an analytical approach based on a more disaggregated view of the GDP.
I think it is clear that, even in rich countries, some components of the economy, such as education, health care, elderly care, and the arts, need to go up significantly. This is true also for organic food production, especially for nourishing foods that many poor people in rich countries cannot currently afford. We must take the impact of income inequality in rich countries into account in our approach to "degrowth." For the rest of the world, the above sectors must increase even more rapidly.
Two other components of the economy that should go up strongly for the next several decades in all parts of the world are the renewable energy sector and the energy efficiency sector. Because of the need to replace existing fossil energy supplies with renewables, and to meet the growth in energy demand that is required in underdeveloped countries, massive investments in renewables and efficiency, net of the decline in the fossil fuel sector of the economy, will likely lead to an increase in GDP. A better way to look at the desirability of GDP growth or decline would be to consider which sectors of the GDP need to grow, which should decline, where and when throughout the world, and for how long. What the net effect on global GDP will be year-by-year over the next few decades is anyone's guess, but it does not really matter as long as people lead ever better and more sustainable lives, and if the world's ecological systems can be restored to health quickly enough to save most disappearing species and to prevent significantly more climate change.
In addition, I feel that the term "degrowth" is most unfortunate from a political perspective, for it is more likely to turn people off from supporting the valid aspects of the politics behind it than to turn them on. Since, by far, most people in the world do not have enough of many goods and services necessary for an adequate and sustainable life, the term "degrowth" will surely convey the intention that they will never be able to have such a life. Yet, given what I have said above, this turnoff is totally unnecessary, and inaccurate besides, relative to what needs to be done. It would be much easier to reach people politically if we make it clear that we need fewer of the "bad" things the world currently produces and more of the "good" things. Then we could focus on the important debate, which is what are the "bads" versus the "goods," how much of each does each region want or need, and how do we get to these goals.