I have a recent macbook for work. The only way I managed to get my 4k external monitor to run at >24 Hz—such a slow refresh rate it was painful to use—was with a $15 3rd-party utility[1]. And that was after failing to fix the problem with hours of debugging and switching from HDMI to DisplayPort.

The same monitor worked perfectly without any configuration on both Windows and Linux.

[1]: https://www.madrau.com/