on an image install there are two partitions, the /boot and the /root partitions
for buster, the /boot partition takes about 250MB (correct me on this), formatted to FAT16
the /root partition takes the remaining capacity, formatted to EXT4.
a full desktop installation, with some bit of extras, will take less than 16GB, so the rest of the remaining space can be used for your data.
however if you're planning to format a portion of the microSD to other formats, its best done on another linux installation (or another raspbian setup)
install gparted and use it to resize (shrink) the EXT4 partition of the microSD
format the remaining to the format you prefer (NTFS, FAT32, etc)
if it does not boot, you may need to edit the cmdline.txt and fstab to temporarily change the PARTUUID=xxxxx-1 and PARTUUID=xxxx-2 entries to /dev/sda1 and /dev/sda2 respectively.
once you've booted properly you can change it back to the new PARTUUID (checked using the command blkid)
I've done this on a 250GB HDD boot RPi3B, which contains FAT16 /root, EXT4 /root and NTFS /data
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