Just for the record - if a device has locked bootloder that can't be unlocked (unlock allowed: no in the service menu) then Sailfish OS can't be installed on it.

Found that out the hard way a while ago when a friend of mine bough a new Xperia X from as it turns out a rather shady e-shop. Apparently if bootloader unlocking is set as not allowed for a device there is no known way around it & it precludes booting any unsigned OS images, including Sailfish OS.

In the end the friend returned the device and is currently contemplating if he should try his luck with another eshop from the dwindling number of shops that sell the X in CZ or wait for the currently much more widely available XA2 to be supported.