In order for the emoji's to work properly on mac OS Big Sur, the window will need to be changed to a popup.
By default, emoji's are accessible in the Character Viewer. Use the Control + Command + Spacebar shortcut to open the Character View.
Click on the menu icon on the far right (next to the search box) to change the window to a popup.
macOS BigSur Keyboard Setting
By default, macOS BigSur uses the Globe key to open the emoji window. This will need to be changed in the Settings > Keyboard preferences. Under the "Press :globe_with_meridians: to" dropdown menu, click and select "Start Dictation (Press Twice)". This option will enable the emoji window to open with Control + Command + Spacebar." add this image to it.
