I have 2 buttons, one is only to open a menu below and the other is to navigate to the view to create a new employee. I recently read an article where they say primary buttons should only be for actions and you should use a link for navigation, which makes sense. Since i have always see in cases like this the use of "primary" buttons i used one, but now im considering changing it, but it just doesnt looks right for me. So which option should i go for, and for the menu button is it okay for it to be a "secondary" button?
The buttons in your second example are perfectly fine (Add Employee seems like a primary action, so the primary button is better than the link-only button in your first example).
I think the tension you're feeling is caused by the combination of a navigation button with a user action button in the same section on the page.
Try to find another location for the Menu button that's at a higher level in the page hierarchy. Here's an example:
Systems should serve users not the other way around. If you feel that the button would be the correct component to place as your main CTA, then do that.
Especially given that it's your primary action. Also, just because you read it in an article doesn't mean it should be followed. Use best practices 'cause they fit your users, not because they are best practices.
Also, last I checked, navigation is an action. So no one should judge you.
The primary button should be related to the main function of the page. Given that it seems "Add Employee" is the main function on this page, I see no problem with using a primary button for "Add Employee". I would redesign your secondary button or create some distance between that and your primary because, as @Izquierdo said, you are trying to place a navigation button next to a user action button. Given how different these two functions are, the secondary button is the problem here.
"Categories" is not a secondary action to "Add Employee". A better example of a secondary action for this is "Edit Employee", but if you wish to have the category function, change the design or placement so that the user does not think that the two buttons are related. Use Gestalt's principle of proximity to get a better idea of why these two buttons must not look like they are related, whether that be in proximity or design.