Some HDR TVs do not have HDR output enabled by default for HDMI.  To enable HDR output from SHIELD, refer to your TV owner's manual.  Here are the settings for some of the common TVs:

• Samsung HDR TVs: Menu > Picture > Picture Options > HDMI UHD Color > On > Restart
• LG HDR TVs: Home > HDMI > Settings > Advanced > Picture > HDMI ULTRA DEEP COLOR > On > Restart
• Sony HDR TVs: Home > Settings > External inputs > HDMI signal format > HDMI [select the SHIELD input] > Enhanced mode (TV will reboot)