This below requirement from Netflix
Both the HDMI cable and the HDMI port on your
TV must be
HDCP 2.2 certified to successfully display Ultra HD content.
This below requirement from Amazon fire stick 4k.
TV Compatibility
1) TV must support minimum HDCP requirements for protected content playback. Compatible with 1) 4K ultra high-definition TVs with HDMI capable of 2160p at 24/25/30/50/60 Hz and
HDCP 2.2 or 2) high-definition TVs with HDMI capable of 1080p or 720p at 50/60 Hz. 4K/ UHD TV required for streaming 4K/ UHD content.