is there a description of the settings? (Red Dead Redemption 2)

You can change any graphics settings through file editing (even if you can't change them inside the game). You can turn on async compute. This will improve the frame of the frame.
You can turn off the grass through the "grassLod value" option. 0.5 is the minimum graphics setting in the game. Negative value of the parameter will completely remove the grass from the frame (grassLod value -0.3)

Maybe there is a complete list of parameters on the Internet with descriptions, which affects? In what ranges can I change?