Froh Qingming-Fest.
The translation according to your meaning is the above German sentence.
But by the way, Qingming Festival is a festival to honor deceased ancestors, which is more solemn and solemn. It is not appropriate to use the greeting "Happy Qingming Festival". Some foreigners translate Tomb-Sweeping Day as the Memorial Day of the deceased (Totengedenktag), so it is recommended that you don’t greet them like this, as it is easy to make jokes.