I’ve rebound Shift-1 and Shift-2 to switch between Action Page 1 and Action Page 2 of Action Bar 1. On my holy priest I put my heals on Action Page 1 and my offensive spells (smite, holy fire, etc) on Action Page 2. Now I can’t find anywhere in the Keybindings where I can set those buttons. So are the 12 buttons on Action Page 2 of Action Bar 1 literally mouseclick only? Because that’s pretty awful 
ugh Never mind. Just realised the spells on action page 1 of action bar 1 are not working either. And when I checked the bindings for them they’re all blank because apparently I’m now using character specific bindings somehow. sigh
Action slots and buttons are entirely different things.
“Page 2” shares the same BUTTONS as “Page 1” (and all other paged bars).
You bind BUTTONS, not ACTION SLOTS.
It’s a PITA and part of why I bailed on the Blizzard UI 15 years ago and use a bar mod.
Yeah I realise the difference between the two, it’s why I spelled out the names in full on my original post. I thought I’d have to rebind the buttons using I dunno… “Action bar 9” or something. Didn’t realise the bindings were literally gone from all my action bars. So pressing “1” did nothing anywhere. Once I rebound actionbar button 1 to “1” it works on all the action pages.
And that’s actually bartenders fault not WoW’s since it rebound 1 to BTActionBar1Button1 or something along those lines.
It’s not Bartender’s fault either.
Any bar mod that made all the bars usable had to deal with the fact that the old interface (and the new) a) didn’t use numeric patterns to identify all the bars/buttons, b) didn’t use the same pattern for all the bars, and c) didn’t deal with the class-specific bars.
In the default (original) layout you could only HAVE 60 unique BUTTONS bound because that’s all that appeared on the screen.
In BT4 and ElvuI and Dominos, you could have 120.
I’m excluding things like pet bars and extra action/boss buttons here.
There are no “action bars” - only “button bars” - and the disparity between those two is why bar mods had to have their own keybinding system if they wanted you to be able to bind every button.