IIRC, the Mahdi as a messianic figure is found only in Shi’a Islam and is disavowed by the Sunni majority who do not even regard Shiites as Muslim.
In Iran they are preparing for the return of the 12th or Hidden Iman (last seen in 960 A.D.) and as Shiites regard him as the final Mahdi.
As for the Ark of the Covenant, if it does appear in public, there will be cataclysmic physical manifestations, IMO.
What lies does Islam have about the origin of the ark?