RMB + Drag disabled

So, I’ve just opened a few of my projects (UE 5.0.1 on Win11) and in all of them, my ability to navigate around the world with RMB+Drag seems to have been disabled.

I presume this is a keystroke that has been inadvertently hit that has changed a viewport mode. I’ve tried changing the editor preferences back to default but this hasn’t changed anything.

RMB works as it is bringing up a menu.

Just a few hours ago opening the same projects all was working fine.