How can I remove a diagram scaling on the left side to align several diagrams to the left screen border or how can I position the y axis on an e x a c t l y defined x-location to align several diagrams among themselves?

There are several purposes imaginable, where you need to “stack” some diagrams among themselves to be able to see the exact situation in different diagrams at the same x position (time, for example), like it is in stocks analysis.
Currently I can’t position the y-axis at an exactly defined location, which makes it impossible to align diagrams to each other.

You say you can’t position the axis at a defined location. What have you tried exactly to attempt that?

I use “Format the axis” to adjust the scale and end-points of the axes on my charts. Double-click on the chart to put it in Edit mode. Left-click on the axis to be adjusted, then right-click on it to bring up the dialog box. Choose “Format the axis”. There are tabs for scale, numbers, font, etc. Many adjustments can be made. HTH.