Not even running WingetUI as admin and then running Upgrade all packages works - or there's been a misunderstanding about the feature.
Regarding update all, I saw it as fetching the latest data - and updating all the apps after that, kinda like scoop update *
(when enough time has passed by obviously).
EDIT: More specifically, the app Icaros, which requires admin, being a non-portable app on Scoop, was in the list, but no matter if I ran WingetUI with admin or not and picked Upgrade all packages, it was always left untouched.
EDIT2: I also noticed it's missing auto-refresh upon updating the packages - after manually refreshing the corresponding apps show up.
Maybe it should simply be a separate button called "Upgrade all packages and install updates".