When I search Google it only shows how to turn it off.
Gmail doesn't have a "turn off spam filter" button anywhere, and never has (unless they were doing some sort of weird A/B test, but I'm dubious they would ever do that). If you saw one, it was likely put there by a third-party. Whether that third-party extension (?) is there to help you with your email, or is malicious and just trying to make you receive spam you don't want.
In any event, what that "button" probably did is create a filter that will match all incoming messages and has the "never send to spam" option checked. You need to delete that filter. You probably also need to re-train your spam detectors by being sure to report spam messages still in your inbox as spam.
Note that there is an administrator function in G Suite that allows administrators to turn off spam filters, but it's not generally available to regular users, and appears in the administrator interface in any case, so that doesn't seem to apply here.