Maybe you have lost focus in that view?
Try shift clicking it twice, once for focus in the view and a second time to remove the selection.
The default mouse select button is left click.
It is possible to change the select mouse button in the preferences to right click select.
Hi Josephine JJosephine ,
Shift+Clicking on a Selected and Active Object, Deselects it, but it still stays the Active Object. Until you SHIFT+Click on another Object, then that becomes the Active and Selected Object, whether that Object was Selected before or not.
It sounds more complicated than it is and it's also something you shouldn't overthink.
oflux @MartinBergwerf @OmarDomenech