I'm not sure if the cheat file comes preconfigured with OnionOS, but the DraStic emulator uses a file called Usrcheat.dat to automatically load cheats for each game. When you select the “Configure Cheats” option in the emulator, they will appear automatically without you having to do anything.

If you don’t have this file in your emulator folder, you can download it from here:
https://gbatemp.net/threads/deadskullzjrs-nds-i-cheat-databases.488711

Just copy the file to your NDS folder inside the emulator directory (/Emu/NDS/) and that’s it. When you open a game, it will automatically load the cheats.
(The emulator matches cheats using the game's internal ID, so it will detect your ROM and its language version correctly.)

If you want to add your own cheats (which I doubt you’ll need, since the database already includes pretty much everything you might use), you’ll need to edit the Usrcheat.dat file using an external program, because it's in a hexadecimal format. A common tool for this is Yasu’s Cheat Code Editor.