Yes man!!! I managed!!! and finally the problem was not related to either the file format, neither the encoder nor the extension or duration of the video...
Just logout and login again without using steemconnect, instead put your posting key!!!
Thanks anyway to all the steemians who tried to help me with this , in particular to @hauptmann , @acesontop , @amico and @brianphobos
btw, I know the video I uploaded here is a piece of Sh*t but, you know, tests are tests!
▶️ DTube
▶️ IPFS