localhost /mnt/efi # mkfs.vfat -F 32 -n EFIBOOT /dev/sdb1
localhost /mnt/efi # mkfs.fat -F 31 /dev/sdb1                                                                                                                             
bash: mkfs.fat: command not found                    

Um diese Befehle zu nutzen muss dosfstools installiert werden

localhost /mnt/efi # emerge -av dosfstools

 * IMPORTANT: 14 news items need reading for repository 'gentoo'.
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These are the packages that would be merged, in order:

Calculating dependencies... done!
[ebuild  N     ] sys-fs/dosfstools-4.2::gentoo  USE="iconv -compat -test" 314 KiB

Total: 1 package (1 new), Size of downloads: 314 KiB

Would you like to merge these packages? [Yes/No] 

localhost / # mkfs.vfat /dev/sdb1
mkfs.fat 4.2 (2021-01-31)

Ist FAT im Kernel aktiv?
= m bedeutet als Modul eingebunden

localhost / # zgrep -e FAT -e DOS /proc/config.gz | sort -r
CONFIG_VFAT_FS=m
CONFIG_MSDOS_PARTITION=y
CONFIG_MSDOS_FS=m
CONFIG_FAT_FS=m
CONFIG_FAT_DEFAULT_IOCHARSET="ascii"
CONFIG_FAT_DEFAULT_CODEPAGE=437
CONFIG_EXFAT_FS=m
CONFIG_EXFAT_DEFAULT_IOCHARSET="utf8"
# end of DOS/FAT/EXFAT/NT Filesystems
# DOS/FAT/EXFAT/NT Filesystems
# CONFIG_FAT_DEFAULT_UTF8 is not set