Can’t delete emails on iPhone 12xr

Which email account are you referring to? Google, iCloud, AOL, Exchange, Outlook, Yahoo or any Other (Refer to the pic )below

1. Is this your corporate iPhone? Then please contact the system administrator of your corporate
2. If it is your personal device, in that case, do you have any profile installed by your corporate/organisation/enterprise/School Management?
   1. Erase the profile added by you If you have installed a profile on your own --> Install or remove configuration profiles on iPhone - Apple ...
   2. Or please contact the system administrator of the organisation who provided the profile to you

You may have enabled two step verification on Google --> Sign in with App Passwords - Google Account Help

You may have enabled Authenticator for Yahoo --> Generate and manage third-party app passwords | Yahoo Help

You may have enbled 2-step verification for Outlook --> Manage app passwords for two-step verification

You may have activate 2-step verification for Aol --> Create and manage third-party app passwords - AOL Help

If you set up your email as IMAP it's syncing with your email server, check if you can delete emails from a client email app, log in your email account online and delete emails from there