Good evening, it is not possible to play in native ultra-wide format (21:9) with the PS5 on this monitor. The PS5 only supports 16:9 format, so you'll have large black bands on the sides of the screen when playing in ultra-wide. You can, however, play in 3440 x 1440 pixel resolution, but the image will be displayed with those black bands on the sides.
As far as refresh rate is concerned, the PS5 cannot use the 165 Hz of the monitor via HDMI. It's limited to 60Hz on HDMI, and even if the monitor supports 120Hz on DisplayPort, the PS5 doesn't have a DisplayPort output, so you won't be able to benefit from 120Hz either.