Is the agreed-upon 20% share of the profits from the flour mill—whose license was issued through personal effort after the father's death—considered part of the inheritance, or is it deemed a special effort of the son who completed the procedures and supervised the installation and operation of the mill?

If the license was issued in your father's name, it is part of the inheritance. You are entitled to a fee for obtaining it if you did so with the intention of claiming it from the rest of the heirs, or if you thought it would be yours. A license that came about because of the deceased is part of the inheritance, even if it was issued after his death. You deserve payment for your work, and what is meant is a fair wage, estimated by experts. This license has a considerable financial value according to custom, so it is permissible to make it capital in a partnership (according to those who permit partnerships with assets in kind). It is necessary to appraise it by knowing its market value by referring to experts, and the heirs will be partners in the business with this value.