Unable to install GRUB. Fatal error.

[NiCoAlloy]

Hello, I'm brand new to linux.
Picked mint as a distro and went about installing it on an old HP laptop.
The laptop gave me trouble because It wouldn't boot from the USB no matter what I changed in the bios.
Secure boot did not exist as an option. So I had to fiddle with legacy boot and UEFI boot options
and boot directly from a .efi

Then within the linux installer I received the following error:
Unable to install GRUB in /dev/sdb
Executing grub-install/dev/sdb' failed.
This is a fatal error.

I resolved this error on my own.
Basically I was installing in UEFI mode without a properly defined root mount.
In the installer, within "something else" I had to touch the following stuff:
The laptop hard drive "sdb" was split in two:
/dev/sdb1 530 MB and
/dev/sdb2 230 GiB
I had to reformat them both to FAT32 and ext4 respectively.
From what I got that's cuz UEFI cant boot from ext4 so it needs a small FAT32 EFI System Partition (ESP) to store GRUB's .efi,
sdb1 had to be used as an ESP,
sdb2 needed a mount point "/",
and sdb had to be the bootloader installation target, ofcourse.
Then the installer refused to recognize sdb1 as an ESP.
Then I learned about gdisk and used it to change the partition's GPT type to ESP with:
" sudo sgdisk --typecode=1:EF00 /dev/sdb "

I'm not entirely sure why this error happened in the first place. I assume its some sort of bug, considering I'm working with an old HP laptop.
So I am reporting it. If someone could explain why this happened, I would appreciate it.