The optimal is 6.75 feet for normal tv viewing at that size.
Optimal is 100 pixels per degree, as that's the point where additional resolution has
severely diminished returns. For a 48″ 4K screen,
that works out to be 5 ft exactly.
no such thing as too close
Personally I find that a 25° vertical (or 60° horizontal) viewing angle is the upper limit for how close I can comfortably sit to any display for an extended period of time - and that's 4¼ ft with this TV.
This might help. Not an expert but seems like it might work.
https://youtu.be/x9n8Hz_RLqw
This is a LTT video
I think this is a better video for discussing the practicality of using a 48" display as a monitor, and issues specific to this OLED:
It does overlook the reduced image quality (lots of color banding) when the TV is in PC mode - though most reviews fail to mention that about these OLEDs.
Having used a 46" display as a monitor for years in the past, I have since found it more comfortable to be using a 34" ultra-wide monitor; but that's partially because the TV was mounted about 4″ above the desk, and had a further 3″ bezel along the bottom edge - so it was too tall.
If I was doing it again, I'd probably mount it to an arm on a height-adjustable desk, so that it could be pushed back against the wall, angled, and lowered to place the bottom edge right on the desk.
You really need a deep desk, and a keyboard arm/tray to make it work well too.