There has been the out-of-tree DKMS hid-nintendo driver to support the Nintendo Switch controller on Linux while with the Linux 5.10 kernel later this year that driver will be merged.
The HID subsystem is queuing the Nintendo driver ahead of the Linux 5.10 merge window expected to open in October.
This independently developed driver allows for the Nintendo Switch Joy-Cons and Pro controllers to be supported under Linux both for Bluetooth and USB mode.
Beyond input, this driver includes supporting the relevant LEDs on the controllers, rumble support, IMU support for the accelerometer and gyro data, and other functionality.
So for those of you wanting to use a Nintendo Switch controller with your Linux games without resorting to out-of-tree code, that will become a reality later this year with Linux 5.10.