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.

Actually works great for me on Opera GX, after the regular adblocker stopped working. That last one did seem to change by the time. YouTube (understandably) seems to try pushing its adds through though. It will probably remain an ungoing battle.

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.