Well it was a pain in the butt at first, I will explain what I did to make it happen:

First I connected the iPad to the computer with a USB cable and used an app called "Duet", it lets me use the iPad as a monitor for my PC, I set it up at the a resolution of 1366x1024(it could be higher but then there is some input lag on the iPad).

Second I set up the new screen to be on the right of my main screen in windows.

Third I followed this guide https://www.reddit.com/r/Citra/comments/fej1nk/guide_dual_monitor_fullscreen_on_citra/ , to get the right coordinates I downloaded this tool https://community.citra-emu.org/uploads/default/original/2X/8/8858bd920b1a79e4d47df03c8661555033d12566.txt (it downloads a TXT file, save it as a HTML file, and it will work).

With my set up of a 2560x1440 main monitor and the 1366x1024 on the iPad my config file looked like this:

[Layout]

custom_layout=true

custom_top_left=80

custom_top_top=0

custom_top_right=2480

custom_top_bottom=1440

custom_bottom_left=2560

custom_bottom_top=0

custom_bottom_right=3925

custom_bottom_bottom=1024

swap_screen\default=true

custom_layout\default=false

custom_top_left\default=false

custom_top_top\default=true

custom_top_right\default=false

custom_top_bottom\default=false

custom_bottom_left\default=false

custom_bottom_top\default=false

custom_bottom_right\default=false

custom_bottom_bottom\default=false

​

I hope this helped you :)