Use Android before Install

[MiKoNu]

Ok, seems I found the cause: the problem in this thread looks exactly like mine:

Xperia 10 ii - Unable to Flash Sailfish X

Yes, the getvar response ‘secure: yes’ means that the bootloader is not unlocked - which prevents installing an alternative OS to the device. But in the report of @unruly, the execution of “fastboot getvar secure” failed which is a different thing.

I don’t have Windows around…
Looks like I’ll have to try on different computers …