Email attachment

Your screenshot shows that you are using a third-party Mail App - whereas the screenshot I previously used to illustrate the expected keyboard was for the native Apple Mail App.

The available controls for the third-party Mail App will almost certainly differ. You may need to seek assistance from the App Developer.

When drafting or reply to an email, you should find the attachment icons at the top of the keyboard. For example, the document attachment button is located here:

Have you updated your iPad to the latest version - iPadOS 15.1? If not, you should do so before considering other fault-finding.