If you’re using gnome disks, it hides the more Linuxy file systems behind an ‘Other’ option.
Personally, for removable drives I prefer to use
ext4 for HDDs
f2fs for SSDs
exfat for Windows compatibility
If it’s grayed out or you’re getting errors try searching up ‘how to format as [file system] in [Pop OS/Ubuntu/Linux]’, you might need some extra packages.