Gocryptfs or CryFS. Many GUI available (Vaults, SiriKali, Plasma Vaults). Android compatibility with DroidFS.

DroidFS does not have Internet permission so any data exfiltration is prevented at the OS level.

Of course, but v1.x only supported gocryptfs. Also, new encrypted file systems may be added in the future.

DroidFS can open existing volumes. Just click on the “+” button in the bottom right corner, then on the folder icon, and then select the volume directory.

To type with only one finger, there’s 8Vim.