Mail app

The question-mark that appears in place of an image or attachment usually indicates content that, for some reason, cannot be downloaded or displayed by the Mail client. The reason why some embedded or attached content may not be accessible are many - and with available information will be impossible to diagnose.

Assuming that you are using the native iOS/iPadOS Mail App, you have two principal alternatives with which to access the content…

1) Most Mail Providers has a webmail portal that can be accessed using a web browser. Sign-in to your mail using a browser of your choice (Safari, Firefox etc.) and view and/or download the content. If the missing content still cannot be viewed, contact the sender.

2) Consider installing a different email App on your iPad. While this cannot guarantee that you’ll be able to access every email that you receive, it can provide a quick and easy alternative access method.

You. might want to try a right click on the question marked attachment, and see if you have an option to view ( or download / "share" to Photos app / or similar) the attachment.

Seems sometimes third-party (non-Apple) apps like ad-blockers, cleaners, etc . can interfere.