From what I see, the 60Hz cap only occurs when VSync is enabled, even when using a high refresh rate display.
Set r.Vulkan.CPURHIThreadFramePacer to “0”, as the code in the Vulkan RHI suggests that it uses a 16.6ms CPU-based framepacer instead of your screen refresh rate. It should then lock to your screen refresh rate if you have VSync enabled (Although there may be some weird oddities when doing this).
Several Vulkan based games on Linux suffer with this issue, and it’s also an issue on basically any platform that supports the Vulkan RHI in Unreal Engine.