Does the complication of a managerial matter, for which supplication has been made for two years despite performing Istikhara, indicate that Allah does not desire it, or is it a test of patience and diligence, and should one abandon supplication or continue with it?

Everything that occurs in the universe is by the decree of Allah the Almighty, and this is supported by texts from the Quran and Sunnah. So, if someone performs Istikhara regarding a matter and it does not transpire, this is an indication that Allah has chosen for it not to happen. Allah may divert something you desire from you and reserve something better for you, for He knows what is best for you, while the servant is unaware of their own interests.