Only a matter of time until advanced civilizations make gunpowder? People worked iron and steel for thousands of years without discovering it. I think the earliest form was a combination of coal dust, sulfur, and saltpeter. This black powder would literally spontaneously explode due to static electricity. Anyways, even after that formula was discovered by pure chancs by Chinese alchemists, it was not used for weaponized for centuries. It took a long time to develop better alternatives and figure out how to use it in cannons and muskets.

All of this is just to my understanding, though. If someone else here is more knowledgeable, feel free to correct me.

In my mind there shouldn't ever be muskets or artillery unless the time period that we cover goes on for centuries, at least. There's also the issue of it ruining the low-fantasy setting, at least in my eyes.