It’s a little annoying to have to Alt+1 3 times just to get a card to the max amount that you play in a non-highlander deck.
I agree but perhaps an idea for the solution is that the website detects which format you are deck-building in and it defaults to adding a number of copies based on the format (4 in non-highlander or 1 highlander)?
When you right click > add more, the default is 3, and you can confirm with enter. So right click > click > enter and you got 4. Doesn’t directly solve your problem, but is a faster workaround.