If I go to my Firebase Analytics Dashboard, there's a "platform breakdown" pie chart that just says "100% iOS".
If I go to "Filter" at the top I can choose each specific version of iOS, but it's super tedious because at a high level I just want to see which version of iOS is being used the most by users.
It's an iOS only app
On the Dashboard under the header "What's your audience like?" which shows a map with where your users are from, you can instead choose the tab "Devices" where you can see the percentage of users on each of your top OS versions.