Thus did We give established power to Joseph in the land, to take possession therein as, when, or where he pleased. We bestow of our Mercy on whom We please, and We suffer not, to be lost, the reward of those who do good.
This is to show that the whole land of Egypt was under his complete control, as if it belonged to him and he could claim any piece of it as his, and there was no piece of it that could be withheld from him. The early commentators have also made the same comment on this verse. For instance, Allamah Ibn Jarir Tabari, on the authority of Ibn Zaid, says that this verse means:We made Joseph the owner of all those things that were in Egypt, and in this part of the world he could do whatever he liked and wherever he liked for he had been given complete authority over this land. So much so that he could bring Pharaoh under his sway and become his master, if he so desired. He has quoted another thing from Mujahid, who is one of the most learned commentators, to the effect that the King of Egypt had embraced Islam through Prophet Joseph.
Maududi, Abul Ala (2010). Tafhim ul Quran. https://www.englishtafsir.com/Quran/27/index.html