Cryptomator is a free and open source software tool that provides client-side encryption for your cloud storage files, available for Windows, Mac, Linux, iOS and Android. The tool, which is very easy to use, supports any cloud storage provider that synchronizes with a local directory, so it works with Dropbox, Google Drive (Google Backup and Sync or whatever Google calls it nowadays), OneDrive, ownCloud, Nextcloud, MEGA, and so on.