It seems like justify text has stopped working on 1.0, it appears always greyed out. I tried to create a text-box and flow in frame but nothing happened.

Thank in advance for your reply,

Justify is only an option for old Flowed Text not for new Text in-a-shape (see status line at bottom of your screen).

https://wiki.inkscape.org/wiki/index.php/Release_notes/1.0#Browser-compatible_flowed_text

Perfect it worked!