If you are looking for a tv to use as a pc monitor, look at the LG OLED units.
I bought a LG 48" CX unit.
https://www.newegg.com/lg-cx-series-48/p/N82E16889007754
The picture is absolutely stunning.
The unit takes hdmi for input.
Al TV's that I know of are only hdmi input.
hdmi2.0 from your graphics card will run at 60hz.
To get 120hz, you need a card with hdmi 2.1 output as well as a 48hz premium hdmi cable.
That essentially means a 3000 series graphics card. Good luck in finding one.
I am still waiting.
On the question of powering up, the unit is essentially instantaneous, 1-2 seconds perhaps.
This is important for one if the issues I have with the unit.
When I sleep the pc, it promptly goes to sleep.
The monitor displays a no input signal found which is normal.
My side monitor, connected with displayport also sleeps normally.
Wake is also quick for both.
The problem comes when left unattended for a while.
In time, the lg will power off.
I have not determined how long that is. Probably 30 seconds, but it could be hours.
If the pc is waked, the side monitor activates, but the lg remains off.
If I use the remote to power on the lg, it activates quickly with one puzzling issue.
The windows that were active on the side monitor now appear on the lg.
If I simply power on before wake, which is only a couple of seconds, then wake happens normally and all windows show up in their proper places.
Bottom line to your question,.....
The lg power on is very quick.