Not unexpected. M-series Macbook Airs have no cooling fans so we see a lot of heat complaints here. Gaming and watching videos are high-demand operations that work the CPU and GPU harder than lesser tasks. Hard work makes more internal heat.
"...bottom area means except screen is turning so much hot..."
See:
Keep your Mac laptop within acceptable operating temperatures - Apple Support
If you are leaving other apps open while watching videos, that also increases heating. Your M1 Macbook Air is convection-cooled like the first iMacs— that also ran hot. Hot air needs to escape and much of it has to exit through the keyboard. For that reason, NO keyboard covers!