I had this problem in earlier versions and have used these settings with my RPI4 and Samsung TV. TV has not randomly turned on since installing 10.1. The only addon I'm using is the Zuki PVR. I always leave the Pi4 on.
Set menu to advanced
Settings > System 1920x1080 60Hz
LibreELEC Add-On PVR/Live TV > General> Use channel numbers from backend
Settings > System > Input > Peripherals > CEC > Switch source to this device on startup > "Set to off"
Settings > System > Input > Peripherals > CEC > Devices to power on during startup > "None"
Settings > System > Input > Peripherals > CEC > Devices to power off during shutdown > "None"
Settings > System > Input > Peripherals > CEC > "when the TV is turned off" > "Stop playback"
Settings > System > Input > Peripherals > CEC > "switch source to this device on startup" from "on" to "off
Settings > Interface > Regional > US > TZ