'Email Myself' shortcut stopped working

For the "From" issue, tap the ">" icon in the Send action. Tap the word "Ask Each Time" (this is why it is prompting you to choose an email address) in the From field, tap Clear variable and the From field should default to your default email address. If not, choose another email address or even choose the magic variable coming from the Email Address action (so that the email is send from and to the same email address).

For the "Allow" issue, tap Always Allow so that you are no longer prompted in the future. (This is a privacy protection.)

The shortcut is missing the Send actions in the If block.

The easiest solution would be to delete the shortcut and to download it again from the shortcut Gallery. In the Shortcuts app, tap the Gallery tab (lower right corner), search for "Email" and grab the Email Myself shortcut.

I just did a test on my iPhone using a 3.3MB file. The shortcut send it without any issues using my Gmail account (for both From and To). I received the email less than a minute later.

I would suggest that you try to send the same screenshot using the Mail app instead of the shortcut, this to make sure that the email sends as expected.

You may also want to restart your iPhone.

Edit: I'm wondering if the issue is with the additional settings in the Send action after tapping the ">" icon. Make sure every field within the Send action is correct.

You are most welcome!