i dont know how big your usb is, but windows iso could be around 4gb … so remove manjaro iso from the usb and replace it with windows iso
its 16gb but when i try and copy the iso over it says ‘the filesystem only supports files up to 4gb’
are you using ventoy on your usb? if not flash ventoy onto the usb, and then copy the windows iso there
iv done that but now im getting this
an error occurred while accessing ‘Ventoy’, the system responded: The requested operation has failed: Error mounting /dev/sdc1 at /run/media/manjaro/Ventoy: Filesystem type exfat not configured in kernel.
and you doing this from live usb?