Infinite growth is possible as long as your economy trades things that are not physically constrained. Art can grow in value over time without hitting any constraints. And even if your economy doesn't grow in real terms, to service debt all you need is for the economy to grow in nominal terms, to have inflation. And even if your economy stagnates completely and has zero inflation you just need to bring your deficit to zero to maintain the debt level. Every year you can just pay the interest on the debt from taxes and your debt as percentage of the economy stays stable without ever paying down the debt.