Amazing Khadas, always amazes you!
VIM4 has an onboard eMMC, so you can install the OS into it.
VIM4 comes with the OOWOW1) embedded service, you can use OOWOW to install your preferred OS directly from the Cloud, which is the easiest way to install OS.
Please check VIM4 Install OS into eMMC via OOWOW.
Please check VIM4 Install OS into eMMC via USB Flash Tool.
VIM4 also supports to boot from external storage, e.g.
USB storage, etc.
Please check VIM4 Install OS into External Storage.