Fastest way to extend notes to fill several measures?

As the title says, if I drop in a whole note, what’s the fastest way to make that take up several measures?

There is a menu item in the “write menu” that does that in the note duration submenu. I have assigned a shortcut to it. You can then select the note and either ctrl-click or shift-click to the desired endpoint and type the shortcut. Very fast!

It’s not perfect but Shift+Alt+Cmd+(right arrow) will double the note duration

If you’re looking to fill several bars, up to the next existing note in a later bar, there’s an option for that too (“Extend to Next Note”).