How did people count before the invention of the number 0?
You don’t need zero to count quantities. Zero is the “nothing” value’s symbol.
You just go about naming every number, like one, two, three, etc., and there’s no limit to it. This is how it used to be in India, which is unsurprisingly the land where the modern placeholder number system was invented.
Here’s a small note on the numbering system, given in Sri Desiraju Hanumanta Rao’s translation of Sarga 38, Kishkindha Kanda, Valmiki Ramayana:1