This is an excellent start to wrist vibrato! Your left hand is doing ALL the right things! And you have a nice shape to both fingers and hand. Now you must become ‘unstuck’ to the neck of the violin at the base of the index finger. A shortcut to this ‘action’ is to eliminate the fingertips touching strings and just practice ‘rubbing’ the violin neck with the spot where your palm/finger touches the violin neck during vibrato. Let this part of the hand move toward you and away from you during a vibrato movement. It will move perhaps between B natural and C sharp as you do this. If this is easy, you’ve got it made~! All you have to do now is add back the fingertips, keep this index base ‘rubbing’ action loose and free. Try it on 3rd finger since this is the loosest and weakest finger. Other fingers present unique challenges to vibrato, but 3rd finger is easiest.
If you had problems, let’s talk again! I’d like to see another video with the base of the index ‘unstuck’ if you can provide it. Good luck!