I hope I can find a solution for my problem. I have a multiple choice quiz and I want the user to be able to continue when he selects the right answers (and that works) but if the user selects the wrong answers or no answers, then he/she should get a permanent feedback that they selected the wrong ones and has to choose the right one.
Thanks in advance!
Very simple: set the Attempts for that question slide to Infinite. Be sure to hide the playbar, and not to insert the Skip nor Back buttons.
but how can I show the feedback when it the answers are wrong?
You have a Failure Message which you can edit. Or do you mean something else by 'feedback'? There is the Remediation feature, which allows you to go to a content slide after a failure. Do you mean that? You can have up to 3 Failure messages on each quiz slide. If the MCQ has only one correct answer you can use Advanced Answer feature. Please, clarify your question.
with "feedback" I mean to show a text for a duration of time and it disappears, then on button click again it shows up, etc.
That is exactly what the Failure message is doing. You can edit that message on each quiz slide. This means that the simple solution I offered from the start is valid.