"/loot ... fish" and "/loot ... loot" don't show all command suggestions, it's being cut off. This does not happen in 1.20.4 and below (I think) and it's seems like it only works for "/loot ... fish" and "/loot ... loot" and not other commands.
To reproduce type "/loot give <username> fish " then pressing the up arrow.
Can confirm.
As a side note, you don't need to keep saying you didn't find any duplicates, since the fact that you reported this in the first place kind of implies that.