It is now well advised to use two separate Storage Drives if you are going to boot both Windows 10 and Linux.
Install Windows on the first Drive but have the second drive disconnected before you do this. After Windows is done installing and updated, reconnect the other Storage Device and install Manjaro. Put each OS’s BootLoader on it’s own drive. To select which OS when booting up, just press the key for the Motherboard’s boot menu.
The reason for doing things this way, is that Windows 10 will not leave other OSes partitions on the install drive alone when updating.
One other thing. Windows and Linux use two different methods for setting the System Clock. Each time you boot into the other OS, the Time will change. Yes you can make both OSes use the same method, but will have to look for the info on the Wiki or Forum.