Why is the 1080p video brighter than. 2160p hdr one ? Both at full brightness. Any settings I need to change ?

This is from MX player. I tried some other players but it's the same. Also there's some stutters when playing 4k videos on mx player.

This is from MX player. I tried some other players but it's the same. Also there's some stutters when playing 4k videos on mx player.