I’m in an 8/8 measure and want two half note chords in the right hand of the piano. However, it will not make half notes but instead is just doing this:
It looks like the bar before is 6/8, right? And you changed the time sig for this one bar?
When you change a time sig in Dorico, it doesn’t add any beats for you; it just rebars the beats that are already there – and it stops when it gets to an explicit time signature, like the 6/8 in the following bar. So it added the 8/8 you asked for, but you only have the 6 beats that you started with.
To add the additional beats, select the last quarter rest in that bar, type Shift+B to open the bars popover, type 1q and hit Enter.
@Vadian has shown how to get the note grouping you want. By default, Dorico assumes that 8/8 is 3+3+2.