Is there a way to make the NOW function in numbers updated automatically?

It can't be done automatically.

The definition of NOW() is that it updates any time there are changes to the spreadsheet. If it kept real-time there are significant questions on granularity (how frequently should it update? per second? per millisecond?), as well as a virtually unlimited number of calculations that could have to happen real time.

If you really need it, you could probably craft a background script that 'tickled' the spreadsheet on a schedule, triggering the update, but there are some significant caveats to consider.

tell application "Numbers"
	tell front document to tell sheet "Sheet 1"
		tell table "Table 1"
			repeat
				repeat while value of cell "A1" is true
					set value of cell "A1" to value of cell "A1"
					delay 2
				end repeat
			end repeat
			delay 2
		end tell
	end tell
end tell

I wrote up an explanation but accidentally deleted it when fixing a typo. Here it is again

Your spreadsheet needs a checkbox in Sheet 1::Table 1::A1

When checked it will recalculate every 2 seconds

When not checked it will wait in the background.

It will quit due to an error if there is no such cell or you close all the open documents or quit Numbers.

Open the Script Editor app. Paste in the code. Hit the "Play" button. You can hit the "Stop" button to stop it.

It takes focus from you everytime it recalculates. It will whisk you away from wherever you are in the spreadsheet and drop you on Sheet 1::Table 1::A1. If you are simply watching something happen this is not a concern but it will interrupt you if you are woking on something.

It is not part of the spreadsheet. You have to start it after opening your spreadsheet. A script can be turned into an app or shortcut or a service (which can be invoked with a key combination) to make this easier.

Change the first Delay 2 to Delay 60 if you want a minute delay. The second Delay 2 is there so it doesn't constantly keep checking cell A1, eating up processing cycles. If you increase it there will be a longer delay for the recalculations to begin after checking the checkbox.