Nintendo has updated Switch system to 19.0.1 to fix the issue with the MAYFLASH GameCube Controller Adapter not being recognized by Switch.
Please update your MAYFLASH GameCube Controller Adapter to the latest firmware version V09 from MAYFLASH web Support page if you still have this issue.
System Compatibility
Switch, Wii U, PC Windows.
Special Features
. Vibration Feedback
. Supports the GC/Wii Emulator Dolphin
. No delay
Includes
GameCube Controller Adapter for Wii U, Windows and Switch . User Manual