They don't have a choice. About a third of Jakarta is already below sea level. It's sinking fast and the rains are becoming heavier and unprecedented more often. About a quarter of the city will be underwater in 25 years.

It's a gamble. Design a new planned city with 60% rainforest now and in 75 years it will be a new metropolis but better thought out and with sustainability in mind while other cities fall into the ocean.

Clearly there's a big gap between greenwash rhetoric and practical reality, but that's not unusual all over the world. The big question here is not the design of the central buildings, but whether it makes sense, as long-term sustainable development, to relocate the capital, and it seems to me there are arguments both ways. Jakarta is low-lying, literally sinking into the rising sea, and the island of Java is overcrowded - so something had to change. The new capital will lead to some deforestation on Borneo, on the other hand by bringing elites nearby they may re-evaluate the value of the jungle, it could be harder to hide destruction. The new location has potential for sea transport, but may lead to an over-dependence on air-transport.
Maybe useful to compare with other countries that moved their capital for geographical balance, and to avoid rising sea-level and overcrowding, for example Lagos to Abuja, or the new egyptian constructions SE of Cairo.