libusbhsfs VS OpenSteamController

Example: https://github.com/DarkMatterCore/libusbhsfs

The OpenSteamController project. The down side is that it’s got a todo list and no updates in 4 years

However, there's an open source project that enables the controller to function on the Switch through cable, basically flashing the controller's firmware so it functions as a generic wired USB controller compatible with the Switch. You can check a video here. I'm not sure if the bluetooth angle would be able to be rewritten so it mimics a Switch Pro Controller or a generic Xinput controller so it can be synced to the 8bitdo dongle tho.

Your understanding is completely wrong, but your conclusion is not.

Here's how I did it last time: https://github.com/greggersaurus/OpenSteamController/blob/master/LoadingFirmware.md

Googling around I saw this post addressing bricked controllers and linking to Valve's Master Firmware list, but the link is dead. Continued googling and found this (Github), telling me to hold down the right trigger all the way which will "activate the USB In-System Programming for the LPC11U37F", but it doesn't.

Did you look up schematics of the steam controller? I suspect the interface to the device controls on the deck will run through USB and be an iteration of the steam controller. https://github.com/greggersaurus/OpenSteamController/blob/master/ReverseEngineering/Luna_maiboard_V000456-00_rev3.md would suggest two pins unused/undetermined. Yes, it's an input device and would require driver/firmware changes, but as long as hardware capability is there, the rest is a software problem.

While it would be theoretically possible to rewrite the firmware (the OpenSteamController project is just this), we've run into this weird situation that, because the SC itself is discontinued, I don't think very many people that would otherwise be willing/wanting to work on such a thing wants to risk bricking their controllers.

It actually is possible to do it. What I did is flashed my steam controller with a custom firmware from the OpenSteamController project. https://github.com/greggersaurus/OpenSteamController/tree/master/Firmware