In previous versions of Dynamics 365 for Finance and Operations (D365F&O), making a field mandatory required a (small) customisation. With version 10.0.0.12 this is no longer the case. Now it is possible to make fields mandatory using personalisation.
In the following example, I would like the Organization number field to be mandatory. To do this, I simply right-click on the field and select Personalisation from the menu. As the following screenshot shows, I can now tick the Required option.

As shown below, the field is now mandatory (red and marked with an asterisks) when editing the record.

Obviously, it is unlikely that an organisation would allow all users to perform this type of personalisation. Since the mandatory (required) field personalisation is saved with the view (in this example “Contoso Customers”, it is possible for an administrator to configure corporate views and distribute them as shown below.

In the above example I am distributing the view to all users in the “Accounts Receivable Clerk” role.
Please note: Instead of right-clicking on the field, the required field personalisation option is also available from the Personalize this page function in the ribbon.
This feature is still in preview, but you can follow updates here.