Procedure
Start with an empty (unpartitioned, unformatted) SD card. If you disk is not empty, you will need to do a search on how to clean the disk and create an
msdos
disklabel (aka partition table).Add boot partition
Gnome Disks while adding a primary partition
Format as VFAT (part of partition-creation wizard)
Gnome Disks add parition wizard format as vfat
Result is a partition formatted as FAT 16
Gnome Disks showing SD card with FAT 16 boot partition
Make the partition bootable
Gnome Disks setting partition as bootable
We want FAT 32 so use terminal to reformat as FAT 32
Drop to terminal to reformat as FAT 32 because GNOME disks doesn’t have that option
Resulting FAT 32 formatted boot partition
Gnome Disks showing boot parition formatted as FAT 32
Mount the boot partition for next steps
Gnome Disks showing boot partition mounted