Hi Sean,
I tested on an android device with d365 app version 4.3.19114.1 without issue.
Have you set the item Type to URL? Have you tried to sign out and sign in again to refresh cache? Is your account security role system admin?
For your customer real requirement,
we could set new lead form as app home page,
first item under My Work area will be home page to whole app.

then when we open sales app it will open new lead form by default.
In addition, my configuration also not worked on my ios phone, it works on android phone with a newly installed app.
So my final conclusion is: Your issue might be caused by cache, because I also met issue on my phone,
you could uninstall d365 app on your phone and re-install it again to remove cache completely.
Regards,
Clofly