Thank you for your support. I am still facing issues. I updated my question accordingly.

Thank you for your response! Seems like this is going into the right direction. Unfortunately, I cannot find the specific dialogue in my QGIS menu (see edited question above).

I want to create a polygon which is colored according to the elevation data provided by the points which I have.

Just one polygon

Thank you for your responses. I tried using the "join attributes by location function". However, the resulting layer only contains one row of attributes. Layer 1 however, contains approximately 900,000 points which I would like to see conserved in layer 2. After all, I want to colorize layer 2 according to the information in the individual points.

Sorry, I just sorted this out in the meantime. You can just draw polygons in a new layer around the points and then perform spatial joints via Vector -> Data Management Tools -> Join attributes by location. Select "contain" as Geometric predicate and select "all records" for joined table. Anyway, thank you very much for your support!

Thank you for your response. Not sure if i got this though. I created an additional layer with polygons which have the same ID as my points. However, if i save the polygon layer as CSV only the ID's are exported. No information about the shape. So if I merge the two CSV files I am actually where i started, or not? A CSV files with points and a lot of attributes but no shapes?