How to construct a chord with different lengths?

I wanted to copy an old cello part into Dorico to enrich the notes with other data.

I do know how to play but not how to write it in Dorico. See the original and what came the closest to is.

You have to enter the dotted half note in a second (down-stem) voice, flip the stems as needed, hide the unwanted rest and adjust the “Voice column index” of the up-stem voice to 1 in Engrave Mode.