On 09 Jun 2021, (Scott Lurndal) wrote in
alt.home.repair:

Many "smart" TV's support CEC device control. If enabled on the
TV, it will automatically switch HDMI ports if or when the device
attached to that port is powered on or changes state.

There is usually a menu item on the TV to disable CEC control either
globally or on a per-HDMI-port basis.

This is usually the cause of unexpected HDMI port switches by the TV.

https://support.google.com/chromecas.../7199917?hl=en

Interesting! My TV does, in fact, have a setting to globally turn CEC
on/off. It's actually turned on now, but I don't have any devices
permanently connected to it to control. I've seen the setting before
but I didn't know what it did.