This is a known issue affecting VMware vSphere 6.7 and later.
Currently, there is no resolution.
Workaround:
To work around this issue, operate all power operations from the original window.
See illustrations below:
Option 1: On the ESXi web application, virtual machine power operations are shown as icons in the row above the list of virtual machines. Click one of the icons ("Power on, "Power off", "Shutdown", "Suspend") to affect the power state.
Option 2: ESXi Host UI > "Open console in new window" > click
Power to view the corresponding operations.
Option 3: On web-based remote console plugin to a virtual machine - click
Power to view the available operations.