This is what I did just now to make my external NTFS drive work: … and thank you for the inadvertent reminder, because I’ve been putting to set this up for almost a year now
Add the line
boot.supportedFilesystems = [ "ntfs" ];
to your /etc/nixos/configuration.nix.
Issue
sudo nixos-rebuild switch
Look up the device name after plugging in the drive with lsblk -f
Filesystems are usually mounted and then the user metadata of the filesystem is applied, though NTFS userdata can not be transfered to the linux model, therefore it assumes everything is owned by root and and usually RO.
If you want to use mount you have to also specify uid and gid options as well as a third option that works similar to a umask.
Personally I consider not using NTFS (permanent mounts) or just using udisks2 (temporary mounts) the best options.
If you’re sharing files between NTFS in windows and Linux, I would recommend using ntfsusermap so windows isn’t confused by access rights, otherwise you can use uid and gid (as others have said) and in combination with umask.