So technically this is not about installing Zorin OS, but rather installing Linux mint.
So here's how it went, in my previous post I mentioned that my only operating system is Zorin OS, and I want to install Linux mint alongside this Zorin OS system.
I plugged in the USB and boot into the USB like normal, until I get to the setup screen.
But he's the problem, when I chose "something else" option, I created some unallocated space for the system and efi partition, but when I created the system partition the unallocated space is now labeled as "unusable", preventing me from creating the EFI partition.
It says that it might be because I'm using an MBR computer, so I have to free up partition, but...I don't think there's any partitions I can remove in this PC...
Here are all the lists of partitions I have: