services.tahoe.nodes.<name>.sftpd.port

The port on which the SFTP server will listen.

This is the correct setting to tweak if you want Tahoe's SFTP daemon to listen on a different port.

Type
null or 16 bit unsigned integer; between 0 and 65535 (both inclusive)
Default
null
Declared
<nixpkgs/nixos/modules/services/network-filesystems/tahoe.nix>