No, it has been documented, well, most of them. For instance is the Maus; we had the hull and the prototype in museum, then the V1 and V2 alongside V3 Cannon; we had the documentary and instance its being used against Allied force, Ho-229; it's in the museum rn, StG-44; it's been used especially by the Volksgrenadier.
The only unproven one and remain as a speculation probably only Die Glocke and Haunebu.

If you refer the name "Wunderwaffe" being actually used or just a term came up by some internet dudes. German actually introduce the term during WW2 as propaganda to boost morale and make people believe Germans were actually winning the war.

I bet you believe the moon landing was faked and the earth is flat too, don'cha?

Idk how you can prove that wunderwaffe projects are fake when they are one of the most well documented projects in ww2

the Maus, V-1 Rocket, V-2 rocket, Graf Zeppelin, Bismarck, Tirpitz, U-Boat and Horten Ho 229