DIAGNOSIS The 5GHz radio module has failed or been disabled. This is a common hardware fault in older R7000 units, often preceded by the router running very hot.
FIX First, check the software setting. Log into routerlogin.net. Go to Advanced > Setup > Wireless Setup. Verify the 'Enable SSID Broadcast' box for the 5GHz network is checked and the network name is set. If settings look correct, perform a full power cycle: unplug the router and modem for 2 minutes, then plug modem in, wait, then plug router in.
IF THAT DIDN'T WORK The radio hardware has likely failed due to heat stress. There is no software fix. Your options are: 1) Continue using 2.4GHz only. 2) Replace the router. 3) Attempt a reflow of the radio chip's solder joints (advanced repair).
HEADS UP If you get a replacement, ensure it has adequate airflow. Placing the router upright (using its stand) significantly improves heat dissipation compared to lying flat.