Alternative way of merging vertices Is there a faster shortcut than Alt+M for merge?
I have seen video examples where it was shown a line dragging from point A to B resulting merge.
It may be an add-on?

Thank you for any of you who will help me!
Ok so real answer is that in the video you link he's using an addon by Pitiwazou and he gives the links in the comments:

https://gumroad.com/l/pie_menu_editor

https://gumroad.com/l/wazou_rmb_pie_menu_v2

Old answer:

Maybe he was snapping a vertex to another one, with the Snap option (Vertices mode) and the Automatically Merge Vertices option enabled? You can even activate the snap tool with ctrl.