This problem that occured after the migration to the new version (v. 7) is now fixed in v. 7.4.4.
Please upgrade and let me know if you have problem.
Right-click on the menu bar and reactivate the widget visualization.
if it does not work close BORIS and delete the BORIS configuration file.
After this you will have to reset all the parameters of Preferences (File > Preferences)
See the manual for the name and location of the configuration file on your system.
To be used with BORIS your video must play well with VLC media player because BORIS used the VLC libraries. The VLC libaries are embedded in BORIS executable versions (except for Linux).
If your video do not play with VLC, you can try to re-encode it.
You can use the embedded tool in BORIS. See Tools > Re-encode/resize video and the guide (http://boris.readthedocs.io/en/latest/#re-encoding-and-resizing-a-video-file)
If your video plays with VLC and not in BORIS you can contact me and send me your video.
If VLC is preinstalled with the snap utility (check with snap list) you will have to uninstall it. Open a terminal and type:
sudo snap remove vlc (your password will be required) VLC must be reinstalled with the apt utility. Open a terminal and type:: sudo apt install vlc (your password will be required)
Use the v. >= 7.9 and lock the dockwidgets on the main window (see Tools > Lock dockwidgets)
You can also check my new project at a very early stage of development DORIS.
It is a tribute to Boris Vian