A few things here:
The button in the top left corner isn’t Escape. The picture on it would suggest that it’s the Hide Invisibles key, or at least it would be if the keyboard was setup as English within the iPad’s own settings and if Dorico was set to use its own English shortcuts.
The keyboard shortcut for inputting an up (cresc.) hairpin is Shift-, (comma), at least in Dorico’s English shortcuts, but I find that I can certainly assign Shift-, to Note Input > Stop Note Input, which is what I’m guessing you want.
All that said, it might just be that you’re trying to assign that key to the wrong function. See Key command UI>Escape doesn’t work for any key that is not the system-wide Esc key - #2 by dspreadbury for instance.