Symptoms
Even "System access management" is unchecked on Client permission page (Plesk, Clients, Client Name, Permissions) , RDP button is available on domain page if client is logged to Plesk under his account.Resolution
"System access management" permission provides option to enable/disable ability for client to manage access to system for domain user on Plesk, Domains, domain.tld, Setup page.Remote Desktop button is always available on domains with physical hosting..