My 2014 MacBook Pro is not able run external monitor at high refreshrate
There is no issue, 60Hz is the highest refresh.
According to the official specifications, that model Mac has a refresh rate of (HDMI)

Support for 1080p resolution at up to 60Hz
Support for 3840-by-2160 resolution at 30Hz
Support for 4096-by-2160 resolution at 24Hz

As for DisplayPort, the released standard for  DisplayPort at the time this Mac was released, was 1.2a.  The maximum resolution and refresh rate was 4K (3840x2160 @ 75Hz) or 5K (5180x2880@ 30Hz).  That doesn’t mean Apple “enabled” those resolutions/refresh rates. They’ve been known to “cripple” features like daisy-chaining which was possible with DP 1.2 but not possible with the MacBook Pro.
The cable may be able to support the bandwidth but, more importantly, the graphics chip must be able to drive that frequency.