are you sure about that? how?
I could not find the magic button to show gpu yet.
I'm using 3.4.1, so it's possible you have an older version that doesn't have it.
btop in contrast, currently shows me: GPU utilization (graph/historic+current), clock speed, power-state, power usage, encoding/decoding utilization, VRAM frequency, VRAM bandwidth utilization (graph+current) + VRAM total/free usage and finally the current transmit/receive rate to/from VRAM.