Select+start to pull up retroarch options, given retroarch hmod is installed. You will then go to settings, video, aspect ratio...after changing aspect, backup to quick settings and apply either game override or core override settings. Beware, wrong button press goes into an annoying, endless search loop (harmless and fixed just by powering off system). Proper one gives no confirmation...But, it will stick upon core and/or game reload.
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Same with system 32 games. Run in 2010, 2014, 2016. But, not 2000, 2003.
2010 and 2014 and 2016 are terrible for the Mini. I used up nearly 100mb of hmod space testing 2014. It is not meant for the Mini, with its limited space.