In Strapi 4.16.2, we can make a normal field required from the admin interface. This prevents us from creating entries, when those required fields are missing, which is very useful.
Now, this feature does not exist for relationships, but we often need to do this too.
Now, we can manually add the "required: true" to the API's relationship, but this actually has no effect, i.e. it only shows the red asterisk close to relationship field (in the content manager), but we can still create the entry without specifying a value for that relationship.
This is actually more a bug than a feature, but may also be feature, in case you never planned to make relationships required.
This is so important. I know many people need this feature. So, please, implement this asap. Thanks.