It may be possible to make do with the following:
1. Draw a small triangle with the Triangle Tool
2. In the Stroke tab, select Align Stroke to Inside
3. Then simply place/snap it on the end of your lines where you need an arrow.
Optional (the following may make a difference depending on your exact intentions with the arrowhead):
4. In the Stroke tab, select Mittler Join (no difference if step 2. is executed)
5. Under Colour/Swatches, make the Fill colour solid (e.g. Black) and remove the Stroke colour.
(see example attached)
I know it's not ideal, and AI does a much neater job (esp. when you need to add arrowheads to rotated lines), but it's what I came up with. Hope it helps.
To AD staff: I hope this does not slow you down in your efforts to add a range of arrowheads soon :)
I also just bought AD as a potential AI alternative 2 days ago, and hit this major obstacle in my scientific (biochemistry) figures.