When I type arrow keys(i.e. down then left) while typing Japanese(refer p1), the same sentence I typed will be added next to the sentence I typed.(refer p2) on Japanese input, there are two steps to input text.
First, type a sentence I want and this is input preview and the sentence will be highlighted.(means it's temporary and not regular text)
Then when I type enter or return, it will be fixed as regular text and highlight on the text will be disappeared.

Usually if I type down arrow while previewing, I can choose predicted sentence below input preview.(refer p3)
But I can't choose predicted sentence on Affinity. While previewing input, commands to manipulate predicted sentence are assigned to arrow keys on Japanese input.
So I'm supposed to be able to choose a predicted sentence with arrow keys.