What were you exactly adding to what type of widget? Were you adding a shortcode to the html widget or a text widget only? Bit hard to see in the video, really. You can add shortcodes to the text and html widget.
The latter (html widget) only though when you added
add_filter( 'widget_text', 'do_shortcode' );
to functions.php of your theme or child theme.
So if you did add it to one of these two widget types and made the code tweak there must have been another issue.
If you however did not add this code to the theme the html widget won’t play nice with the shortcode.
Perhaps the issue was more about the html you actually added. This as it seems the issue was using a text widget..
So we need to know more about what you were trying to do exactly here..
