Let’s see if it works
Use List.Flatten after all nodes.
# Phython-Standard- und DesignScript-Bibliotheken laden
import sys
import clr
clr.AddReference('ProtoGeometry')
from Autodesk.DesignScript.Geometry import *
clr.AddReference("RevitAPI","RevitServices")
from Autodesk.Revit.DB import *
import RevitServices
from RevitServices.Persistence import DocumentManager
from RevitServices.Transactions import TransactionManager
doc = DocumentManager.Instance.CurrentDBDocument
elements = UnwrapElement(IN[0])
vertical = IN[1]
horizontal = IN[2]
if not hasattr(elements,"__iter__"):
elements = [elements]
TransactionManager.Instance.EnsureInTransaction(doc)
for el,ver,hor in zip(elements,vertical,horizontal):
el.HorizontalAlignment = HorizontalTextAlignment[hor]
el.VerticalAlignment = VerticalTextAlignment[ver]
TransactionManager.Instance.TransactionTaskDone()
OUT = elements