Cryptomator
Cryptomator is an open sourced FILE LEVEL encryption software for end-user devices.
Cryptomator iOS client software is not free so is not suitable as an universal solution that scales out to cover everyone, but it is open sourced and its integration with iOS Files app adds an easy to use end-to-end encryption layer on top of Infinite Disk SMB which also works through the iOS Files app.
Cryptomator for Windows, macOS, Linux, Android client software are free and open sourced at the time of writing and should work with Infinite Disk through SMB or WebDAV.