Or simply reach peak population growth which is a common occurrence on the small scale. With population at a steady state, there is nothing GDP needs to outgrow.

If population is steady,GDP still must grow. Otherwise, most of the people who get ahead/gain a better life will do so at the expense of another. That is not a nice world to live in.

Except interest rates. Things would be nicer if our economy didn't depend on paying back interest with economic growth.

Why would a business need the loan in the first place if it doesn't expect a return?