[Vuejs]-Dynamically adding counter to v-data-table with two buttons to increment and decrement and the number between them

Looks like you have only one counter variable, which is used in all rows. Try adding the counter to your coin data, or if you do not want to change those, add a separate coinCounter object which stores counter by coin key (coin.symbol). It should look something like this:

<v-btn icon x-small text @click.stop="coinCounter[coin.symbol]++">...

or

<v-btn icon x-small text @click.stop="coin.counter++">...