Jq: how to extract from map of maps?

I have

{
    "version": 2,
    "clients": {
        "c1": {
            "updated": "0001-01-01T00:00:00Z",
            "instances": {
                "i1": {
                    "updated": "2023-03-19T17:45:03.703984279+01:00",
                    "chargePower": 349.9999940395355
                }
            }
        },
        "c2": {
            "updated": "0001-01-01T00:00:00Z",
            "instances": {
                "i2": {
                    "updated": "2023-02-10T18:34:56.352428175+01:00",
                    "chargePower": 0
                }
            }
        }
    }
}

and would like a map of instance id (i1...) and the map it has associated like this:

{
    "i1": {
        "updated": "2023-03-19T17:45:03.703984279+01:00",
        "chargePower": 349.9999940395355
    },
    "i2": {
        "updated": "2023-02-10T18:34:56.352428175+01:00",
        "chargePower": 0
    }
}

I get as far as

.clients | to_entries | .[].value.instances 

which gives

{
  "i1": {
    "updated": "2023-03-19T17:45:03.703984279+01:00",
    "chargePower": 349.9999940395355
  }
}
{
  "i2": {
    "updated": "2023-02-10T18:34:56.352428175+01:00",
    "chargePower": 0
  }
}

but fail to convert that back to a map. Here's a jqplay: https://jqplay.org/s/FMnrrUIV27U

.clients | with_entries(.value = (.value.instances | to_entries[0].value))

Will update the value of the key with the first value of instances

{
  "c1": {
    "updated": "2023-03-19T17:45:03.703984279+01:00",
    "chargePower": 349.9999940395355
  },
  "c2": {
    "updated": "2023-02-10T18:34:56.352428175+01:00",
    "chargePower": 0
  }
}

Not sure if I got your question right (it is lacking the expected output), but if you are looking for an object with the instances' keys as keys, then you could use map on the parent objects and add on the resulting array of nested objects:

.clients | map(.instances) | add

Or a reduce-based approach:

reduce .clients[].instances as $i ({}; . + $i)

Output:

{
  "i1": {
    "updated": "2023-03-19T17:45:03.703984279+01:00",
    "chargePower": 349.9999940395355
  },
  "i2": {
    "updated": "2023-02-10T18:34:56.352428175+01:00",
    "chargePower": 0
  }
}