Apparently, the main measure of economic growth is the gross domestic product - "the monetary value of all the finished goods and services produced", which is based on spending and consumption. Planetary entropy, as you say.
As someone else commented in this thread, what we need is a significant global shift in mentality and culture, our value systems and vision of what it means to be a grown-up civilization, not as an ever-hungry consumer, but an intelligent layer of nature.
Agreed, though whether we have time for this to happen seems doubtful. It would require a dramatic slowdown of faux-growth to enable natural systems to recover, while we spend the time needed (probably centuries) to develop tech with sustainability approaching that of evolved systems. There's no a priori technical reason why this should not be possible, but political realities make it hard to imagine. Maybe another 'intelligent' species can make this happen in a few millennia.
Life on earth is only possible because we're receiving a constant flow of energy from the sun.
Surely, we should not expect exponential growth, but it doesn't mean we could not have unlimited growth.
How so? It's not an argument per se - it's just a description of the physical reality that what economists falsely describe as 'growth' is actually a transfer of matter and energy from complex evolved sustainable systems (ie. what some people call 'nature', which I find to be misleading) to simple cultural-technological unsustainable systems. This transfer process damages the former to build the latter, increasing entropy (because our early-stage human tech is less ordered than evolved systems are). It is not 'growth' in any meaningful sense of the term at all, whether limited or unlimited.
Even limited 'growth' has not actually happened. It's a fiction. The physical reality is that complex sustainable evolved systems have been broken down to feed simpler crude unsustainable techological ones. There's no 'growth' to be seen - just an increase in planetary entropy. This is somewhat masked on a short-term & local scale because of the remarkable resilience of the evolved systems. But as those systems collapse, which now seems inevitable, the fictional nature of 'economic growth' will become very evident indeed.