I have an input:

$ ip -json route show > ip_routes.json
$ cat ip_routes.json # I've pretty printed this for easier reading.
[
  {
    "dst": "default",
    "gateway": "10.1.201.1",
    "dev": "eth0"
  },
  {
    "dst": "10.1.201.0/24",
    "dev": "eth0",
    "prefsrc": "10.1.201.74"
  },
  {
    "dst": "10.1.202.0/24",
    "dev": "eth0",
    "prefsrc": "10.1.202.74"
  },
  {
    "dst": "10.244.0.0/24",
    "dev": "cni0",
    "prefsrc": "10.244.0.1"
  },
  {
    "dst": "10.244.0.0/22",
    "dev": "cni0",
    "scope": "link",
    "flags": []
  }
]

I can do a query where dev is eth0 and not the default gateway:

$ jq '. [] | if .dev == "eth0" and .dst != "default" then . else empty end' ip_routes.json
{
  "dst": "10.1.201.0/24",
  "dev": "eth0",
  "prefsrc": "10.1.201.74"
}
{
  "dst": "10.1.202.0/24",
  "dev": "eth0",
  "prefsrc": "10.1.202.74"
}

If I try to select specific properties in the output their association with the object is lost:

jq '. [] | if .dev == "eth0" and .dst != "default" then .dev, .prefsrc  else empty end' ip_routes.json
"eth0"
"10.1.201.74"
"eth0"
"10.1.202.74"

How do get something like this?

[
  {
    "eth0",
    "10.1.201.74"
  }
  ,
  {
    "eth0",
    "10.1.202.74"
  }
]

https://jqplay.org/s/GsAwBlKJJ92DNAO