
In order to have access to the touchpad and motion functions, the quadstick needs to be in PS4 mode with the authentication turned off.
For basic controller stuff, default PS3 mode also works.
Mouse and keyboard to not pass through the FGC2 to the console.
On the PS5 side,
the PS5 controller settings should be set to wired USB only and disabling the PS5's Bluetooth. This prevents the native Dual Sense Controller from periodically waking up and taking over the connection via Bluetooth.
Some people report using the front USB-C connector via an adapter to USB-A female worked more reliably than the USB-A connector or the connector on the back.