the others who are working mechanics can explain better than me, but before you get to the "shark teeth" point, the space or dip between each tooth gets worn deeper and wider, so when you put a new chain on, this accelerates chain wear----now how much and how fast this happens, I dont think photos on the web of a chainring can show this.
I know that when a new chain is put on a bike, and you do that "pull chain away from chainring" test to see how much space shows, an experienced mechanic can eyeball it, but I dont have the expertise on this, and anyway, this is internet diagnostic, so only can do so much.

all I can say is that when a cassette is worn enough that skipping can happen with a brand new chain, my experience shows that the cassette can still look fine at a glance, ie no specific shark tooth going on

so we come back to being aware of monitoring chain wear, I use the "1/16 rule over a foot" thing, as my point of reference to change a chain. An old bike of mine went to a good 2/16ths after years of commuting and ignoring measuring, so needed a new cassette at that point.

or you do like friends of mine do, ignore chains, clean grindy paste off once a year to feel better, and dismiss the "change chain at 1/16th" rule as not needed, and ride their bikes on same chains forever, cuz they wear together and "dont skip", so they are content. (until they one day gripe because a bike store tells them they need a new chain, new cassette etc, but hey, you can lead a horse to water, but........)