It looks like you are using a custom rig. Custom rigs do not retarget with the demo animations so you will need to provide your own animator controller. This page has more info:
The arms use a generic model setup so they require the animations to be created specifically for that rig and cannot use Unity’s animation retargetting . . .
Hello, Justin, thanks for the answer In your example FPS Mesh Tool just cut off hands, and then custom rig used and it works I just don't understand, why ? Because, we are using also custom rig and it's the same as in your asset. There is no way how we can add our hands to your FirstArmsController ? We should replace it with our controller and your controller works only with hands from asset ?
FPS Mesh Tool works because it is using a humanoid rig. Unity can retarget animations with a humanoid rig, but it cannot with a generic rig. The demo first person animations use a generic rig so for first person animations you will need to create your own animations that work with the rig that you are using. This is a restriction within unity rather than the controller.
Thanks a lot, Justin, for this explanation. So, for now the best way for us is just make our arms with humanoid rig, apply to them not "FirstArmsDemoController", but "Demo" controller, and it should work