I am relatively new to ModelBuilder. I am trying a basic task using the merge function. I have a folder which consists of a lot of shapefiles. Each shapefile from the folder needs to merge with file 'Punkte.shp' (if it is a point), 'Linien.shp'(if it is a line) or to 'Flaeche.shp' (if it is a polygon). What mistake have I made in my model? It is important that I get the output file with name (inputfile_) corresponding to the input file name from the data. I tried with iterator (Iterate Datasets and Iterate feature class), both has shown error. I have only Basic version of ArcGIS Pro.
I would say your model logic is flawed. Look at the help file to see that the Merge tool takes a LIST of datasets as input. Your model is attempting to run the Merge tool on every loop of the iterator. This is a very inefficient way to run and will likely cause problems.
You need to read the help file and understand what the collect tool does and sub-modelling. There are many examples on this site.
I would have a sub-model that collects only the point data and creates a LIST of point datasets that feeds ONCE into a merge tool which is in the master model.