Hey. Im using Manjaro. I want to install Windows 10 and use it as dual boot. So every video I seen on Youtube has Windows, then installing Manjaro. But I have Manjaro then install Windows. So it kinda confused me. Should I install Windows 10 for full disk, then install Manjaro? Thanks.
Windows is notorious for always destroying any existing boot partition it finds on the machine. Best to pull the power/data line from existing Manjaro installation first.
Support for Windows is off-topic and therefore of no concern to Manjaro Forum and thus there’s no good answer to the question as theres is too many unknowns.
Theoretically - if your system is equipped with two disks - then maybe it can be done - I would recommend to disconnect the disk with Manjaro - to avoid accidents.
If your current system is MBR you cannot install Windows without destroying Manjaro.
If your current system is GPT/EFI you may have a theoretical chance of success - again - it is unsupported - and you may loose ability to boot Manjaro - but - you have a theoretical option to boot a live Manjaro then setup grub config for os-proper and restore the bootloader gaining access to both Manjaro and Windows from grub.
There is simply too many theoreticals - sorry - we cannot help you.
The closet thing we have on Windows is how to successfully install Manjaro in tandem with an existing Windows.