[Hreflang question] When serving a single sub-domain for a certain region but not a specific country is it sufficient to set Hreflang to x-default?

Situation:

Subdomain to serve as main landing page for certain region.(lets use africa) Example. Website/africa/index.html

This is the english and default version.

Would it be ok to just set default hreflang to the above site?

Im fairly certain there is nothing wrong with this but im just trying to be sure.

Digital marketing agency in darbhanga