Question Is 65 Brightness Level okay for an OLED Monitor ?

OLED is prone to the burn-in regardless the brightness of the monitor.

It has been tested in-depth. Just need to use Google a bit.
Test data + results: https://www.rtings.com/tv/learn/permanent-image-retention-burn-in-lcd-oled

If you look at that data, you can see OLED burn-in started to show itself as little as 6 weeks mark. With 20 hours per day usage, that's 140 hours per week, whereby burn-in stated to show after 840 work hours. At 10 week mark, or 1400 work hours, burn in is so severe that it will get into the way of normal usage of a monitor.