Is it possible to add a custom made .svg to Arc GIS Pro line feature. I made a custom arrow, which I want to add. I know it is possible when you are using point data, but I haven't seen the possibility when you use line data.
Side question: at the end I want to link the .svg to the data but I don't know if it is possible to maken graduated symbols of the .svg.
You can add a marker symbol layer from SVG to appear at the end of the line.
In the Symbology > Settings tab, Add a marker symbol layer:
Then, in the Symbology > Layers tab, insert shape from File:
Add your SVG file and modify as required in the Marker Placement setting further down this tab.
With regard to scaling. You can scale proportionally, but I don't think you can link the marker symbol size to field atrributes in a graduated symbols way.