This is applicable to the Android and iOS "Flow" apps. What's expected is that all "Date" input fields that become available throughout the entire app should use a Calendar control to select the correct date, much like Flow through the browser on Desktop. This is to save the user having the enter a date manually in the "YYYY-MM-DD" format which, while being the ISO8601 standard, is not a format all user are comfortable entering dates with.
Here's the original bug report verbatim:
Create a flow that starts from the Flow Button (shows as Manually trigger a flow)
Click "+ Add input"
-> Run this newly created flow on your Android or iOS device and tap on the Trigger Date field
-> You will notice that no Date Picker / Calendar appears. Instead, the software keyboard displays on-screen and expects you to enter a date in YYYY-MM-DD format.
-> Run this newly created flow on your desktop machine and click in the Trigger Date field
-> You will notice a Date Picker / Calendar appears for easy use