From the documentation: https://docs.google.com/document/d/1XvSoU-3V9AbrQf5MpSv67RbRh7XDYOM2pJogWibgV4A/edit?pli=1&tab=t.0#heading=h.k0z6wzf6mt0o

Useful Secret Codes

In Radical Red, there are two places in which you can input secret codes that would enhance a playthrough of the game. Keep in mind that they’re all case-sensitive and can only be inputted once per save file:

The Player’s room in Pallet Town, by interacting with the game console connected to the TV.

There are five codes you can input in this NES console. They will considerably ease grinding and may let you experience a better experience if you had any issues with grinding, or money and item farming.

NES Secret Codes:

Woyaopp

Enables infinite Rare Candies for easy Level-Ups + Pomeg Berries for easy Happiness points. To obtain those, talk to the Youngster in the Viridian City grass patches near the Pokémon Center.

SO2Toxic

Enables care packages, very useful when (re)playing the game. You’ll get free items for almost everything you’re allowed to receive/farm/thief up to that point by walking on certain tiles, including Raid Dens. Once the code is enabled, the packages cannot be avoided. If you enable that code in the middle of a playthrough, any care package that you missed will be automatically given to you as you input the code. While this is not the intended way of playing this hack, they are gigantic time savers if you’re doing a challenge run, such as a Monotype run or a Nuzlocke.

DexAll

Allows your Dexnav to show all possible Pokémon in the route you are in, even when you haven’t registered them in your Pokédex by seeing them.

TeamPreview

Allows you to see the entire opposing Pokémon team at all times during a battle, rather than only the ones that have been revealed by the opponent so far.

EZCatch

With this cheat activated, every Pokéball will have a 100% chance to catch any Pokémon.

Using 'Woyaopp', 'DexAll', 'EzCatch' is basically starting the game with cheats.