How to grant a subscription user SSH access to its home directory?
To allow Plesk users manage the option Access to the server over SSH in their panel, enable the option Management of access to the server over SSH at Service Plans > plan_name > Hosting Permissions.
Use the SSH Terminal Plesk extension to access the server from the Plesk interface.
The feature to provide SSH access to a particular directory (for example,
/var/www/vhosts/example.com/httpdocs/) is not implemented in Plesk yet. If you would like to see this functionality in Plesk, vote for this feature on Plesk UserVoice. The top-ranked suggestions are likely to be included in the next versions of Plesk.