The option key does not work to switch to bootcamp. The MacOS boot volume is not in the Windows partition

When I restart the computer (a MacBook Pro Touch-Bar 15 inch 2016 running 10.14.4 Mojave) and holding down the Option key, the computer simply starts under MacOS. It does not access this "switching" screen. How can this be corrected?

Yes: I reset the NVRAM memory several times

Yes: I can always start manually on Windows via the startup disk. The problem arises when I load in Windows 10 and that it can not restart in the Mac part because Windows can not load the Mac OS boot volume.

The Mac portion perfectly recognizes the Windows portion, but not the opposite.