Using Popups Too Often
Popups are an option to set the spotlight on important information. With all the cookie banners and special offer popups, we see popup fatigue and users try to work around them.
Popups can have a drastic improvement on conversions if you place them strategically. I like combining popups with heatmaps to see where on my landing pages there is some kind of action.
Keep in mind that you don't need more than 2-3 max popups for your entire site. Less is more in this kind of scenario