Mplexhete.club is one of a multitude of potentially unsafe websites created to make the user receive unsolicited advertisements. The way Mplexhete.club goes to achieve that goal is through push notifications. While getting bombarded with annoying advertisements is less than ideal, Mplexhete.club can't do it unless the user expressly allows Mplexhete.club to display notifications. If the users click the "Allow" button, they will be on the receiving end of a barrage of advertisements pushing whatever the creators of Mplexhete.club want to. Generally, the user will receive advertisements promoting adult content websites, online gambling websites, and potentially fake downloads for application updates or freeware.
There are countless websites like Mplexhete.club.. The common thing is that when a user allows one of those sites to display notifications, the advertisements will pop-up even if the user's browser isn't open. Fortunately, removing the permission doesn't require a lot of expertise. The specific steps the user needs to take may vary depending on what browser they are using. However, ultimately, the users need to open the list of websites they have given permissions to display notifications. Then they need to find Mplexhete.club and remove the permission. Another option is to download any reputable security suite and let it solve the problem.