Notes 4.0 (El Capitan) strikethrough option removed
Solution 1:
Yeah, the option is a bit well hidden, dunno why. Its called Struck through instead of strikethrough
To get the text formatting in Notes 4.0
1) Make a text selection for the struck through, right click on it
2) Select Fonts then Styles
3) Use the Style Browser or whatever that is called to check the Favourite Styles and then select Struck Through from the dropdown list. Tada!
Wow. That was really easy and accessible, right? Why not add another step since all that makes a lot of sense. I guess, this time Apple struck through the UX.
Here one close-up of the option. I think one can make a Keyboard shortcut that will make this more ehh sane to use. Maybe there is one already.
Solution 2:
I believe that ⇧⌘L is intended to replace striking items through. This provides you with a very nice list that you can check and uncheck items. It is annoying that they would bury the strikethrough, but I do enjoy the checklist a lot more, especially when viewing the notes on my iPhone or iPad.
Solution 3:
To add on to PJJ's answer, you can more quickly strike through text with the copy style keyboard shortcut. Select some already struck through text, Opt+Cmd+c (Format > Font > Copy Style). Then select the text you want to strike through and Opt+Cmd+v (Format > Font > Paste Style).
From: Has anyone figured out a keyboard shortcut to globally strikethrough selected text in any OS X app?