Exponential growth can be sustained for millions of years, see life on earth.
Moore's law lives on in GPUs and TPUs.
Link: https://www.biogeosciences.net/3/85/2006/bg-3-85-2006.pdf
The resource usage of all the doubling time periods until the last one would have used up only 50% of the resources available(this could be millions of years, depending on the exponent), and then suddenly the last one would use up all the resources left.
This is repeatedly exemplified in Professor Allen Bartlett's talk "Arithmetic, Population and Energy"(video link at specific point: https://youtu.be/sI1C9DyIi_8?t=1337 transcript: http://www.albartlett.org/presentations/arithmetic_populatio...)
Notice how life on earth is plateauing...