I have found a solution regarding the lidar files for NRW and Qgis and would like to provide my solution here for everyone who, for example: build a route for NRW. First of all, I would like to thank RobertSchulz, who gave me the idea of simply using elevation data. I hope I can help some of you The PDF file can be found in the appendix.
Nice, that you could make it finally! Altough I don't know how much I really helped here. I think you found the right way at least after all the stress with it. Yes, Lidar data are I guess better than sticking with the SRTM data. And especially for Nordrhein-Westpfalen, which has high quality LIDAR files available for free, it was the right choice to invest time and nerves into the solution to the Lidar problem in QGIS.
Well nice guide but sadly i dint come far... I came to where it has to be merged i did just that but after that i dint know what .tif file you were talking about and i wasnt sure where to create these folders could you give me some help with that? Idk if im the only one who has this problem... maybe its just me and im too dumb i dont know...