Unable to log in as the Magento user in Filezilla

Firstly thanks for the Youtube videos they have been super helpful!
I’m unable to log in as the Magento user using Filezilla and keep getting the error.
|Error:|FATAL ERROR: No supported authentication methods available (server sent: publickey)|
|Error:|Could not connect to server|
I want to use filezilla to create the directories and files for a custom theme.
if i login as my sudo user i can browse the files but I cannot add, or edit anything in the /var/www/html directory as its owned by the Magento user
Its probably something obvious but im stuck!

as a temporary solution I’ve changed my Magento user to a sudo user and added the same ssh key as my regular non root user but im not sure if this is a bad idea for security purposes or not ?