Yes, there's a very small chance that I might miss a feature that I care about. However, there's a 100% chance that if I read your popup, I'm not spending that time doing something else that I know I want to do because I consciously chose to do it.
And let's not pretend that it's just 5 seconds this one time. Website and app behaviors like this eat up 5 seconds load time on a slow phone, 5 seconds to read, 30 seconds to remember what you were doing before your attention was hijacked, 3 minutes and $10 to add data to your phone plan because you used up all your data, over and over and over again. Because lots of sites do this, and that time and loss of attention adds up.
So frankly, I don't care about your ad for your new feature (and let's be clear, it is an ad). I'd rather have the 5 seconds and other things you're taking from me with that What's New section, and if you do this kind of thing consistently, I'll go elsewhere.
[1] https://medium.com/@tristanharris/how-technology-hijacks-peo...