If you installed #RetroArch on an Apple TV or intend to do it, here's my feedback of a couple of days using it, and how I solved some problems that I ran into.
RetroArch is an emulator that's been recently made available on #iOS, #iPadOS and #tvOS. It can emulate a variety of consoles and computers. Up to now, I've only tested Playstation 1, Amiga and Super Famicom.
The first thing you want to do after pairing a Bluetooth joypad with your Apple TV and launching RetroArch is to assign at least two shortcuts. For that, go to Settings>Input>Shortcuts and assign joypad buttons to display/hide the menu and to quit the app. It's important to quit the app properly at least once, so that the settings you changed get saved, otherwise the settings would be reset to default.
To import your ROMs, use a browser from your computer, phone, etc. It must be connected to the same network as your Apple TV. The URL to go to is displayed in a popup when you launch RetroArch. Once you get there, go into the "Downloads" folder, create a new "roms" folder and upload all your ROMs into it. Create a subfolder for each machine you want to emulate.
To emulate a Commodore Amiga, you must get the kickstart file corresponding to the Amiga you want to emulate (A500, A1200...) and upload it to the "System" folder of RetroArch. As for the Playstation, you won't have to upload additional files if you choose the "ReARMed" core to run games. Same with the Snes9x 2010 core. If a core needs some additional files, it will display a message anyway.
After uploading the roms, you can go to "Import content" and scan the content of your roms folder. It will add an additional menu entry for each machine.
One bug that I ran into is that RetroArch started crashing each time I tried to run a game that wasn't associated to a core. Normally RetroArch should ask you which core to use instead of simply crashing. I solved that problem by deleting RetroArch and re-installing again, starting from scratch.
Also, an important thing to keep in mind is that, due to the way the current limitations of tvOS, all the data of RetroArch are stored in a cache folder and are considered temporary by the system. This means that if your Apple TV runs out of disk space, it could delete those data. So make sure you have enough available space on the disk of your Apple TV to prevent that.