I reported this on 2.3.4.117 but never heard anything and it still exists in 2.3.5.125.
Trying to create a trigger on a "Custom Attribute" for a keypad using "Any Value" produces a screen in the UI with no option to save the trigger--only a "Cancel".
Workaround is easy: Select *changed* as the Comparison; that will reveal the Done With This Trigger Event button. Then change it to **Any Value**, the Done button will still be there: