OLED panels don't have fixed max brightness, a better panel simply has better endurance at higher brightness.
So for example if one panel can do 1000 nits for 200hours and end up with 95% original brightness
And another panel can do 1000 nits for 300 hours and end up with 95% original brightness
then the latter panel is better, which you could use to run it at say 1200 nits. But you could also just run it at 1000 nits for longer.
System integrator ultimately has the say on whether they want to use the better panel for more brightness, or more resistance to burn-in.
Also brightness works in logarithms, meaning 1200 nits would look almost the same as 1000 nits, you need to like double the brightness before there can be an appreciable increase in perceived brightness. But doubling the brightness would usually quarter your panel life and more than double the power consumption. So unless you're desperate, you really really do not want to run high brightness on OLED.