The correct syntax is cryptsetup luksChangeKey <device> <key file>. So what you tried is opening a file that is named like your new passphrase. Such a file of course (hopefully) doesn't exist.
Just omit the last parameter, i.e. sudo cryptsetup luksChangekey /dev/nvme0n1p3 and enter the new password when it asks you to.
The correct syntax is
cryptsetup luksChangeKey <device> <key file>. So what you tried is opening a file that is named like your new passphrase. Such a file of course (hopefully) doesn't exist.Just omit the last parameter, i.e.
sudo cryptsetup luksChangekey /dev/nvme0n1p3and enter the new password when it asks you to.