I have flaired this as fan labor because that's what this was. A hell of a lot of work by many people to figure this mess out. Edit: Apparently the mods don't agree with my classification ¯\_(ツ)_/¯

If you're like me (hella ausquistic B) ), and you want to keep your muscle memory from the first version of this game that you played the hell out of, you are out of luck by default, because Capcom hates you and thinks little enough of your intelligence to only let you choose presets for the controls, all of which suck ass. You have to choose one to work with, so for now go with the default, number 1.

So, what we have to do is find the .ini file that controls the inputs. You have to do this in desktop mode. It should be located in /home/deck/.local/share/Steam/Steamapps/common/Resident Evil 4/BIO4 . You will need to enable the option to view hidden files/folders. I forget exactly where that is, so I'll edit this part Later™ when I refresh my memory. It's not terribly hard to find as long as you're at least a little bit tech literate, which, if you're here, you probably are.

Once you find the input.ini file, you will realize it makes no goddamn sense, so now you have to decipher it. Thankfully, others have already done a lot of that work for us: https://residentevilmodding.boards.net/thread/770/adjust-controller-configuration

The problem in the steam deck is that, when you remap the deck's X button to be nearly anything other than confirm/fire like it is by default, it stops working. Sometimes you'll get one half or the other of the functionality you wanted, but never all of it, so we're going to have a somewhat different control scheme than the one they set up above. We're going to essentially be ignoring the X button and replacing anything that needs it with a different button. This affects the other buttons' functions, so we'll have to remap those, too. If you just copy and paste what I have below, you should be good. If it doesn't work, let me know and I'll upload it on pastebin or something. I don't promise to be fast though.

This is for ###XINPUT_CONTROLLER_A

KEY_FORWARD = QKEY_GC_B4
KEY_FORWARD = QKEY_GC_B20
KEY_BACK = QKEY_GC_B3
KEY_BACK = QKEY_GC_B19
KEY_RIGHT = QKEY_GC_B2
KEY_RIGHT = QKEY_GC_B18
KEY_LEFT = QKEY_GC_B1
KEY_LEFT = QKEY_GC_B17
KEY_KAMAE = QKEY_GC_B5
KEY_RELOCKON = QKEY_GC_B7
KEY_RUN = QKEY_GC_B10
KEY_FIRE = QKEY_GC_B9
KEY_ASHLEY = QKEY_GC_B7
KEY_CK = QKEY_GC_B9
KEY_KAMAE_KNIFE = QKEY_GC_B8
KEY_ST = QKEY_GC_B13
KEY_OPTION = QKEY_GC_B13
KEY_C_U = QKEY_GC_B24
KEY_C_D = QKEY_GC_B23
KEY_Y = QKEY_GC_B12
KEY_X = QKEY_GC_B14
KEY_B = QKEY_GC_B10
KEY_A = QKEY_GC_B9
KEY_SSCRN = QKEY_GC_B12
KEY_MAP = QKEY_GC_B6
KEY_LB = QKEY_GC_B7
KEY_RB = QKEY_GC_B6
KEY_U = QKEY_GC_B4
KEY_U = QKEY_GC_B20
KEY_D = QKEY_GC_B3
KEY_D = QKEY_GC_B19
KEY_R = QKEY_GC_B2
KEY_R = QKEY_GC_B18
KEY_L = QKEY_GC_B1
KEY_L = QKEY_GC_B17
KEY_Z = QKEY_GC_B5
KEY_Z = QKEY_GC_B8
KEY_EV_CANCEL = QKEY_GC_B13
KEY_CANCEL = QKEY_GC_B10
KEY_OK = QKEY_GC_B9
KEY_OK = QKEY_GC_B9
KEY_LL = QKEY_GC_B1
KEY_LR = QKEY_GC_B2
KEY_LD = QKEY_GC_B3
KEY_LU = QKEY_GC_B4
KEY_C_R = QKEY_GC_B22
KEY_C_L = QKEY_GC_B21

Ashley is mapped to the left bumper (B7), and the in-game function of X, which is to say, picking stuff up in the attache case, is mapped to select (B14), of all things. Run and cancel are mapped to B (B10). This isn't all, however, because pushing select every time you want to pick something up is fucking dumb. So what did I do? I remapped the buttons in steam input. This is unfathomably stupid, but it is the only solution I have found for a GameCube-like layout on steam deck, and I'm glad we have the option. Steam input is unbelievably powerful, so it's the only reason I was able to actually make all this work.

https://steamcommunity.com/sharedfiles/filedetails/?id=3043434591

https://steamcommunity.com/sharedfiles/filedetails/?id=3043434652

I have also uploaded it as a layout on steam deck, though I need to update it. F1 is for RE4Tweaks. You are going to want that. You will want to set the right trackpad (or left I guess, if you'd prefer) as a mouse, and R Trackpad click as left mouse click. This will make it where you can actually change things in RE4Tweaks instead of just getting to look at it when you push F1. You will also need to set QTEs to automatically complete. I don't yet know if combat QTEs will autocomplete, but if not, you're gonna have a bad time, because we are literally missing the X button with this. If that's the case, you may be able to just set R4 as the combination for like, X A I think it is, and have each command set as turbo so when you hold the button it counts as rapidly pushing both buttons. When I get to the Big Cheese I will know for sure and be able to make tweaks to make everything work... I hope.