Thank you so much @gohlip and everyone who helped me here. Y’all guys are awesome
The cause of the issue was the installation from a VM. @petsam was right that I should just install it properly from an “actual” live CD (or bootable USB), which I did just now, so now I got both drives with working Manjaro installed (and it’s pretty awesome ).
Lesson learned: “Always install a distro from a proper live CD, or bootable USB pendrive.”
You see, I’m only using the virtual machine (VM) method cause I don’t have an extra flash drive to create a bootable USB or burn the ISO to a CD. Since the method worked for Xubuntu and elementary OS, I decided to try it as well with Manjaro, but it failed and lead me to create a post here. But now I found a way around to avoid this type of installation method after searching for a while.
I ended up using an app called DriveDroid. It allows a PC to boot from ISO/IMG files stored on the phone. This way, I am able to boot from my Android device and install Manjaro properly. My beloved savior
I’m still a noob in Linux, so thank you guys again for helping and guiding me here (and also, understanding my bad communication skill )
It is still unclear to me why the method worked for the two distros I tried but not with Manjaro. Is it a thing between Debian and Arch installation? Anyway, I’ll leave this all here. But if anyone wants to debug and see through this, just notify me