This feature is not so simple to implement, as it involves enhancing IPrefs. We decided to leave it for a future update as there were more important things to resolve first. Priorities are a must when there is such a big to-do list and limited manpower.
In the meantime, users should just resize their desktop wallpaper to the resolution they need using third party programs, which exist even on AmigaOS. Between many others, we can safely recommend dtscale24 by Thomas Rapp:
https://thomas-rapp.homepage.t-online.de/download.html
A pre-scaled background will also significantly decrease loading time and will therefore be the fastest solution in any case.
