jq ' from_entries'

cat data/ann.json | jq '.metadata.annotations | to_entries | map(select(.key == "label1" or .key == "label2")) ' cat data/ann.json | jq '.metadata.annotations | to_entries | map(select(.key == "label1" or .key == "label2")) | from_entries' 
[
  {
    "key": "label1",
    "value": "stam"
  },
  {
    "key": "label2",
    "value": "another"
  }
]
    
{
  "label1": "stam",
  "label2": "another"
}