Firefox, and even Edge, has this feature as well.
I understand it is not groundbreaking, but it sounds too simple to not implement. Especially since it does not conflict any other features.

My usecase:
As a web-developer using Opera (GX), I would like to configure where my devtools would be located when working on a landscaped size browserwindow (e.g. right) or a portrait size window (e.g. bottom).

This way I don't have to manually change its location when moving my window from one (rotated) monitor to the other (not-rotated).

Firefox, and even Edge, has this feature as well.
I understand it is not groundbreaking, but it sounds too simple to not implement. Especially since it does not conflict any other features.