subdivide fill and merge

Hello. Can you give us a time stamp on the video? Also walk us through what you are doing so we can see where the issue might be. 

Hi Ismail @shola_expert  ,

I guess you are talking about ~3:15. (please, add a timestamp next time).

Do you, by any chance have Emulate 3 Button Mouse enabled?

Anything else, that is not default (for instance Addons)?

Check preferences for where ALT might be enabled to emulate middle-mouse functions. If Emulate 3-button mouse is enabled, Alt will create a different function. 

Another thing that might be enabled which would mess with this default hotkey is under Keymap in preferences - Alt Tool Access. By default, that should be switched off, and can create an issue with the hotkey demonstrated.