came up with something like this in the advanced mode query tool. Is this the right way?

{
  "env": "prod",
  "firstOpen": {
    "$gt": 1644728400
  },
  "$or": [
    {
      "$and": [
        {
          "phoneOS": "ios"
        },
        {
          "nativeApplicationVersion": "1.1.5"
        }
      ]
    },
    {
      "$and": [
        {
          "phoneOS": "android"
        },
        {
          "nativeApplicationVersion": "1.1.2"
        }
      ]
    }
  ]
}

The other option is like you said, have two separate rules, one for iOS and one for Android, each running an A/B test and use the same tracking key. The conditions would be much simpler so you wouldn't need the advanced mode at all.

A 3rd option is to add a new attribute that contains both the os and version. If you are going to make rules that need both a lot it would make things simpler:

{
  "env": "prod",
  "firstOpen": {
    "$gt": 1644728400
  },
  "osAndVersion": {
    "$in": [
      "ios 1.1.5",
      "android 1.1.2"
    ]
  }
}