DIAGNOSIS The TV is stuck in standby, likely due to a failed mainboard or a corrupted internal software state that's preventing the full boot sequence. The red light means it's getting power, but the brains aren't waking up.
FIX First, unplug the TV from the wall. Press and hold the physical power button on the TV itself (not the remote) for 60 seconds. This forces a hard reset and can clear any temporary memory glitch. Plug it back in and try turning it on. If that doesn't work, try a panel refresh: unplug the TV, press and hold the power button on the TV for 30 seconds, then plug it back in while still holding the button for another 30 seconds. This sometimes jolts the system.
IF THAT DIDN'T WORK If the red light still won't change and the screen is dead, it's probably a mainboard failure. This is a known, albeit not super common, point of failure on some LG OLEDs. You'll need to contact LG support for a warranty repair or board replacement.
HEADS UP Don't just keep it plugged in and cycling power with the remote. If it's a mainboard issue, that won't help and the constant failed boot attempts can sometimes cause other problems. A full unplug from the wall is the key first step.