Unless you purchased the Surface Pro 11 FOR BUSINESS, your SP11 was most likely supplied with Windows 11 HOME, which cannot join a domain. The consumer version of the SP11 is Snapdragon (ARM) powered with Windows 11 Home, while the business version is Intel powered with Windows 11 Pro.
If you have the consumer model with Home, you would need to upgrade to Pro in order to join a domain.
When the setting you reference is greyed out, it indicated the OS is the HOME version