WinRT: I can click on the corresponding icon (a buble with " inside) but then, the mouse cursor disappears while the file picker page is shown and VLC is frozen while sound is still running in the background.
Subtitles need to be selected quickly (to be in time to "freezing"). Then, at worst (if is frozen" after subtitle choice), it is necessary to click the Enter key (for activation selected).
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information