Using classic Outlook for Windows in business environments
Same here, very bloody annoying.
Started happening about two months ago and no way to stop it.
I use reading pane (right) and scroll message to message, when I click anywhere in the two line view, it opens the email in a new window and I have to manually close it.
Happens to me using latest Outlook Desktop client
Microsoft® Outlook® for Microsoft 365 MSO (Version 2306 Build 16.0.16529.20226) 64-bit