You need to define a /home partition and some GB of a swap is maybe helpfull too.
The home partition is, where it loads the whole system into for the user settings.
If you still use your hdd, you can bind your home folder into the system.
Second, you need to tell it, where grub should be installed at.
Linux never used fat32. This is only a microsoft specific filesystem. Linux always use ext/ext4 nowaday.
Fat32 is only needed for the EFI bootloader.
So you need to use your free space to make a root-, swap-, home-, and efi boot partition.
When you scroll down here to Manjaro installation, its shows you how to make it.
Even i would not shrink a partition, what contains datas, at least, not, before i did backup them.
https://forum.manjaro.org/t/root-tip-dual-boot-manjaro-and-windows/1164