max refresh rate on m2 pro with displayport

Depends which one and what Rez, 10 or 12 CPU...

Display Support:3 Displays*Resolution Support:6016x3384 (6K)*

Details:*This model supports "up to three displays" -- two displays up to 6016x3384 (6K) at 60 Hz over Thunderbolt and one display with up to 3840x2160 (4K) resolution at 60 Hz over HDMI.

Alternately, this model can support "up to two displays" -- one display with up to 6016x3384 (6K) resolution at 60 Hz over Thunderbolt and one external display with up to 3840x2160 (4K) resolution at 144 Hz over HDMI or one external display up to 7680x4320 (8K) at 60 Hz or 3840x2160 (4K) resolution at 240 Hz over HDMI.

The Thunderbolt 4 ports support native DisplayPort output using USB-C as well as Thunderbolt 2, HDMI, DVI, and VGA output with adapters.

8 CPU...

Display Support:2 Displays*Resolution Support:6016x3384 (6K)*

Details:*This model supports "up to two displays" -- one "up to" 6016x3384 (6K) resolution at 60 Hz over Thunderbolt and one display with "up to" 5120x2880 (5K) resolution at 60 Hz over Thunderbolt or 3840x2160 (4K) resolution at 60 Hz over HDMI.

Apple doesn't promise anything higher than 60 Hz for Thunderbolt or USB-C( DisplayPort ) connections. Whether there might be unadvertised support for higher refresh rates if resolution is low enough, I don't know.