Need help in setting up Encryption & Decryption of file in AWSS3 using React JS (Electron) w AWS KMS

We use S3 to share large number of files. These files are uploaded from one instance of React JS - Electron application and downloaded on another instance of same application for a different user. We want the files to be encrypted when uploaded to S3 and decrypted when downloaded on another instance. Sender will share a key with receiver to decrypt the files.

Note: Please share your experience related to KMS and Data keys in AWS, this will be use to send and receive encrypted files