I confirm that the brightness issue has been solved by installing nvidia-driver-510 from https://launchpad.net/~graphics-drivers/+archive/ubuntu/ppa for my Lenovo Legion Y7 laptop, known as Y9000K in mainland China.
However, the problem where the sound disappears when waking up from suspension is still present.
System:
Host: jizong-Legion Kernel: 5.16.4-051604-generic x86_64 bits: 64
Desktop: GNOME 40.5 Distro: Ubuntu 21.10 (Impish Indri)
Graphics:
Device-1: NVIDIA GA104M [GeForce RTX 3080 Mobile / Max-Q 8GB/16GB]
driver: nvidia v: 510.47.03
Device-2: Acer Integrated Camera type: USB driver: uvcvideo
Display: x11 server: X.Org 1.20.13 driver: loaded: nvidia
unloaded: fbdev,modesetting,nouveau,vesa resolution: 1: 3840x2160~60Hz
2: 4096x2560
OpenGL: renderer: NVIDIA GeForce RTX 3080 Laptop GPU/PCIe/SSE2
v: 4.6.0 NVIDIA 510.47.03