Note about Inkscape 1.1
In Inkscape 1.1 there is a bug that positions circles and rectangles incorrectly during export to ILD Render.
They can also disappear completely when they are outside the viewport.
A workaround for this is to convert these objects to paths.
To do this select the objects ⇒ Menu Path ⇒ Object to Path

It is recommended to update to inkscape 1.4

run the ILD Render installer again

or

if you've installed ILD Render already:
run the ILDRenderPluginInkscape.exe
it is located in

C:\Program Files\ILD Render\Inkscape\ILDRenderPluginInkscape.exe

The above path may be localized, e.g. C:\Programme\.. in german windows.