@anthem212 well there are three commands to turn off the output

vcgencmd
dpms

these two turn off the HDMI port, NOT the monitor/tv

and cec-client

this turns off the monitor/tv
IF it supports the cec command(correctly)

and then you would need a people sensor,
most use use infrared, as it’s ‘easy’.

there are modules that put all this together.

search here for MMM-PIR

Now to get your speed requirements will be a little harder. I use TV’s for my two main mirror systems. 43 and 55 in.
one supports cec, the other doesn’t.
when I turn off the HDMI port on both, they put up a big NO INPUT screen , and power off after 15 minutes.
that is energy star compliant.
but you can’t turn them on via software

if it supports cec, then maybe you can turn off/on via software. mine is inconsistent. always can turn on, but not off
on is the same as pushing the button, takes 15 seconds, displays the product logo and all that.

I gave up, and just hide the mm content and leave the TV’s on. the one in the hall I call the nightlight!

I also use a webcam for motion detection, instead of pir, cause that’s what I had at the time

as yours is a 4k tv, I’m guessing it supports cec

install the cec-utils package on pi
sudo apt install cec-utils

this also only works on my pi 4. not pi3.