that is going to be difficult......
not sure is this will show up, but search at REI for bikes 12 to 20 lbs all in the $3000 to $3800 range
https://www.rei.com/c/road-bikes?ir=...2%20to%2019.99
4 show up in 20 to 25 pound range $1000 to $2000
this salsa is 25 lb and $1000
https://www.rei.com/product/128510/s...laris-700-bike
this rei bike is 23.2 and $2000
https://www.rei.com/product/159860/c...es-adv-23-bike
bottom line your expectations are not reasonable
IMHO best bet for 20 or under and under $1000 is to find a vintage high quality steel frame and put good components on it. Bikes like an 84 team miyata or an 84 torpado super strada speced out at right around 20 lbs (i have had both and been close to 20lbs without a weight weenie build)