I sent in a version of this as a support request, but I thought it would be useful to repost this issue here in case others are experiencing it. Setup details and full description of issue is below.

TL;DR

Nintendo Switch Pro Controller connects successfully to Apple TV and is almost fully useable in Steam Link app/with games. HOWEVER:

1. the Start/+ button doesn't work and the Steam Link app doesn't register any input from it, even when remapping controls in app.
2. the square screenshot/clip record button on the Switch Pro Controller shows as mapped to both the Guide AND Start buttons on the Gamepad display in gamepad settings, but only functions to bring up Steam Overlay
3. nothing appears to be remappable in Steam Big Picture mode; buttons can only be remapped in the Steam Link app, where the Start/+ button input isn't recognized

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I am experiencing an issue utilizing a Nintendo Switch Pro Controller (SPC) with the Steam Link app on my Apple TV. I have listed the setup details of my PC, AppleTV, and Network below, followed by a description of the issue I'm facing.

Hardware Info:

Network:
- Xfinity Gigabit Internet Plan
- Motorola Surfboard DOCSIS 3.0 Modem
- Apple Airport Extreme Router (Tower)
- TP-Link AV2000 Powerline Adapter - Ethernet over power adapter

PC:
- Running Windows 10
- Latest version of Steam installed
- Hardwired to network via ethernet direct to router

Apple TV:
- Apple TV 4K (1st-gen) running Beta tvOS 16 (running beta because of added SPC support)
- Steam Link app installed and up to date
- Have confirmed that the SPC connects to Apple TV successfully over Bluetooth and works properly to control tv/play Apple Arcade games
- Hardwired into network via ethernet over Powerline Adapters (confirmed working)

Things that are confirmed working (results are reproducible):

- Switch Pro Controller (SPC) connects to Apple TV
- SPC can be used to launch Steam Link app
- Steam Link app connects to host PC
- Steam Link app recognizes the SPC as a connected gamepad
- Using the SPC, I can:
_1. Start a remote session in the Steam Link app
_2. Control Steam Big Picture mode
_3. Launch and control Games
- Games run extremely well, with almost no visual latency and no controller input lag; the controller performs most in-game functions as expected.

MAIN ISSUE - Things that are confirmed NOT working (also reproducible):

The start button (+ button on the SPC) does not work. It doesn't map to anything useable on the SPC. This renders certain games as completely unplayable (ex: Monster Hunter Rise runs beautifully and has no input lag, but I can access the main menu screen at all in game because the Start/+ button doesn't do anything). Furthermore, when I try to remap controls, either via the Big Picture Controller Layout screen OR the Controller button map list, I am unable to reassign any of the inputs. If I back out into the Steam Link app main menu, and go to check the gamepad button assignments there, the Start (+ button on Pro Controller) does not register to any of the inputs on the Gamepad visual shown on screen. However, the button that serves as the screenshot/record clip button on the Nintendo Switch Pro Controller (small square button located left-of-center on SPC, right below the Select/- button), if pressed, shows as mapped to the Guide AND Start buttons on the on-screen Gamepad visual.

I realize this is likely something that will have to be debugged and worked on as the Apple tvOS 16 is still in beta, but it would seem there's some communication issue between the Apple tvOS and the Steam Link app that both improperly maps the Start/+ button on the Switch Pro Controller AND prevents inputs from being remapped.

Is there anyway around this?