It can back up to device - internal or SD card, to attached USB OTG drive (I believe), or to the cloud. It’s still rubbish though - failing to backup many apps, and failing to restore some apps that it claims to have backed up.
Better backup solutions are available: checkout the solutions in this wiki post. They won’t backup ‘EVERYTHING’ , but they are the best I’ve found.
It’s a command to check, if OEM unlock is active or not (I found in the internet).
I think if I don’t get an answer, it may be impossible to sideload.
I’m going to try your way. If it’s not possible, I will flash stock ROM and afterwards iodeos again… Tomorrow…
Hopefully I’m able to restore my seedvault backup from SD card 
Hi,
As you probably know, some fastboot commands tend to vary from a manufacturer to another one. Maybe this one is not integrated in FP’s bootloader.
What’s your output for :
> fastboot flashing get_unlock_ability
If it’s 1, it means that OEM unlocking is enabled, and you can unlock your FP’s bootloader.
When it’s unlocked (including critical), you can flash FPOS directly with their utility.
Then you can boot (or not) into FPOS. And re-install correctly iodéOS.
If you need any help do not hesitate to ping me. You can also ask help in the Matrix channel: Matrix iodéOS channel
WebDAv or Nextcloud is possible.
But for me not stable not reliable.
I use the Seedvault backup and back up locally to the device, and then synchronize the local backup folder with FolderSync to a cloud. Alternatively, a sync (with FolderSync) to a local computer would also be conceivable, with SMB to a shared folder …