In the Classic Outlook (the Win32 application), the software allowed you to force "Single" view (which shows headers) even when the reading pane was on the right. However, the New Outlook is hard-coded to force "Compact" view whenever the reading pane is placed on the right. In Compact view, the application collapses the From, Subject, and Date columns into a single "card" to optimize space, intentionally removing the headers. This is a design constraint of the current build, not a missing setting or a user error. No amount of troubleshooting within the New Outlook interface will produce those headers while the pane is on the right because the code for that layout simply does not exist in this version.
If this specific workflow (Right Pane + Headers) is critical to your daily operations, the only technically valid solution is to revert to the Classic Outlook. You should see a toggle switch in the top-right corner of the window labeled "New Outlook" (currently set to On). Please toggle this to Off. The system will ask for feedback; you can skip this, and it will relaunch the Classic Outlook application. Once you are back in Classic Outlook, you will regain the ability to have the reading pane on the right while retaining your column headers, exactly as you had them before.
VP