FYI a retail version (i.e. no need of developer mode) of retroarch is now available for Xbox:
https://www.microsoft.com/en-gb/p/retroarch69/9mx29m0p7rqc?rtc=1&activetab=pivot:overviewtab
FTP app for transferring files:
https://www.microsoft.com/store/apps/9NKPZMQ8R1MR
On Xbox One, retroarch used to struggle with Gamecube/Wii games but on Xbox Series X, the emulation seems near perfect. Even 4K resolution seems to work well. However, the motion control of Wiimote are a bit difficult to perform with the XSX controller. If only the XSX controller had gyro.