Make sure you already installed the latest Boot9strap and Luma CFW and have a firmware of 11.4 or higher.
Rename any existing boot.firm in the root of your SD card to boot.firm.bak in case you want to go back, then drag the boot.firm from Luma3DS 9.0 - Plugin loader.zip into the root of your SD card
Place the contents from ActionReplay.zip into either

sd:/luma/plugins/<Title ID of the game folder>/
- Name of the plugin must be plugin.plg if placed here.
or sd:/luma/plugins/ActionReplay/
- Name of plugin must be ActionReplay.plg if placed here.
- if placed here allows loading the plugin for all games if no specific plugin is found.

Either download or clone this repository or search in the cheats folder for the game you want to cheat on and download the .txt file in the folder
Move the .txt file to either

sd:/cheats/
- txt files are conveniently already named correctly if placing here
or place along side plugin.plg from #4 and rename the .txt to cheats.txt

Use your button combo to load up rosalina menu (default is usually L+Down+select) and enable plugin loader if it isn't already and then load up your game

If you get a green screen during load then it worked
To open CTRPluginFramework menu press select once in-game and click on Action Replay button to see the cheats.

Note: The plugin loader is automatically enabled on Old3DS because Mode3 games needs it.
Note: On N3DS, you have to enable the plugin loader from Rosalina, and you can disable it too. You can't disable it for Mode3 games though.

If you decide to want to use LUMAS3DS 9.0 Plugin Loader alongside with BOOTNTR follow from the first step otherwise start at the second step!

Make sure to disable the plugin loader from Rosalina if you're using the boot.firm of Luma3DS with Plugin Loader
Download ActionReplay.zip

Make sure you already installed the latest Boot9strap and Luma CFW and have a firmware of 11.4 or higher.
Place the contents from ActionReplay.zip into SD:/plugin/<Title ID of the game folder>/
Either download or clone this repository or search in the cheats folder for the game you want to cheat on and download the .txt file in the folder
Move the .txt file to either

sd:/cheats/
- txt files are conveniently already named correctly if placing here
or place along side plugin.plg from #4 and rename the .txt to cheats.txt

if you get a green screen during load then it worked
To open CTRPluginFramework menu press select once in-game and click on Action Replay button to see the cheats.

How To Add Cheats Using CTRPF AR On 3DS

After following either of the above you can look at this video to see how to use the editor and create codes and/or you can follow below.

Press ActionReplay
Press the Circled Plus Icon
Press Code
Name your Cheat
Press the Pencil Icon on your currently added cheat
Press Code
Press L or R to add a 1 line of code, Pressing Y will delete the currently chosen line of code

While on the currently chosen line of code, Pressing L will add a 1 line of code above it, Pressing R will add a 1 line of code under it

Then type the code you want to add using the Touch Screen
For N3DS only: Pressing ZL Will copy the currently chosen line of code to be pasted using L or R, And Pressing ZR will Clear the Clipboard

When done Adding/Editing code, Press B to go back and Press A to Mark a Check/Activate the cheat, and leave the cheat menu and see if the cheat works
Also there's a Help on the Options inside the Code Editor in case you didn't notice it

If you wish to contribute

codes that the CTRPF AR supports(Same as Gateshark but with more options!): link

NOTE: I didn't create these cheats, and some cheats might not work.
- If a cheat is not working, it just means that the cheat is wrong: no support will be done for cheats not working, I'm not here to fix all cheats, if you need help with broken codes either make an issue or add a comment in this thread and somebody may be able to help you. Thank you!

Put them inside a text file called cheats.txt or <Title ID of the game>.txt.

Put them in SD/plugin/<Title ID of the game folder>/cheats.txt
If you're using the Luma Plugin Loader, Put them in SD/luma/plugins/<title ID of the game folder>/cheats.txt
Or put them in SD/cheats/<Title ID of the game>.txt

Can I use both cheats.txt and <Title ID of the game>.txt files at the same time?

No, you don't/shouldn't use both if you already have 1 .txt file for the game in one of the directories. You only need either a cheats.txt or <Title ID of the game>.txt for a game not both.

LUMA3DS 9.0 Plugin Loader only recognises CTRPF (AR) Plugins called plugin.plg and ActionReplay.plg
Make sure your using only 1 CTRPF (AR) Plugin! And No Other Plugins included alongside it! (Such as Gateshark2NTR, libshark2NTR or any other Plugins).
If it gives you error, try Deleting the CTRPFData.bin if it exists.
If you can't find a game you are looking for, you can try Max Cheats or GameHacking and see if they possibly have it.

Extra Notes to myself

Games - Inazuma Eleven 3 (EUR), Teenage Mutant Ninja Turtles (USA) and (EUR), Shovel Knight (EUR) and (USA), LBX - Little Battlers eXperience (EUR) have 2 different .txt files. I Need to look into this.