so friends, thought i would add a twist in here, i ran into the same problem and reinstalled after applying 16.3 but found that the mail app would still open in a black screen. there apparently was also new terms and conditions for me that i had to accept, which when i did then everything worked good. i have seen this behavior for years, when an update comes out if the app (or something indirectly) is updated then it seems to be an all good or all fail. try to login to a non-ipad device to accept the terms if you can by going into settings > mail. >unchecking mail > waiting a minute or so then reselecting mail again and you should be prompted to accept. once that is done, then try to go back into your ipad, close the mail app fully and reopen and waalaa, all good 🤙🏾 if it was your phone (in your case), use your ipad on icloud web, you just need to access on another device that is not the device having the issues.