jq ' from_entries'

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