How do I hide the mail sidebar in iPadOS 26 on my iPad in portrait mode?

It appears you can’t. However, double-tapping a message in the list opens it in a separate window

Samax65 wrote:

Then to close that mail you need to tap top left to enable tapping the red close button. I presume pre release testing found this acceptable.

Given the extensive beta testing Apple does, I'd say that's correct.

You can let Apple know that you don't agree with this decision here:

Product Feedback - Apple

Then to close that mail you need to tap top left to enable tapping the red close button. I presume pre release testing found this acceptable.

Not on my iPad. Double tap does nothing

Working now. Thanks

How was this “feature” to disable toggling off/hiding the message list sidebar? So unhelpful for folks who need larger fonts for reading email.

Another bad choice by Apple. Not only is Steve Jobs dead, he's still dead.