That is a very broad generalization. First of all inflation is not just some co-product of economic activity. It has specific reasons. An economy is not stagnant because the oil price sinks after geopolitical tensions ease. An economy is not stagnant because businesses are kept from price gouging in cartels or monopoly situations.

Also “stagnant” is not inherently bad. The reason why we need economic growth is because the super rich are siphoning off more and more wealth, so economic growth is the only thing keeping poor people from revolting. A zero growth or even degrowth economy could serve the people very well, if wealth wouldn’t be hoarded away by select few.