What lead magnets can be used to gain subscribers to UI/UX newsletter?

Hello everyone. I want to dedicate the next year to a big project, related to UI/UX. I haven't decided yet what it should be, asked product hunters here https://www.producthunt.com/discussions/what-is-missing-in-the-educational-ui-ux-market and still not sure. So if you have any ideas, I'd VERY much appreciate it. However, apart from this, I need to get subscribers. Not for blunt ads promotion or something like that, but to be sure that even if the product I did is not brilliant, I'll have a loyal audience that will be willing to buy it. Right now I keep on sending more or less good articles (without ads at all, except my books occasionally), here http://user-interface.io/ But I feel like making a lead magnet to increase the subscription base is an easier task that can be achieved quickly. But on the other hand, I don't want it to be like "Hey, here is a checklist of top 20 UI/UX mistakes, want to get it? leave your email". I want to find a sweet spot between making something interesting, and politely asking for a subscription if people are interested in it. One of the superb ideas that a folk recommended to me is making a good UI test. The key feature ot the test is: 1. In the beginning I promise to give away my book for free (which is decent, I mean, it has something, not a 5 pages book). But only if you answer all the questions correctly 2. If you answered them, I ask for your email, saying that you'll be subscribed, but I don't send any spam 3. If you failed the test, I'll recommend subscribing to the newsletter to learn new stuff so that you don't fail next time Of course users can try to pass the test many times and finally win the book, but I plan to use one of the books that I've already sold a lot and it's not the biggest one, so it's not a big deal. But can you think of any other ideas? Once I made a site about the history of UI that went viral (https://history.user-interface.io/), and people loved it. But I can't think of any other ideas that can be more or less quickly implemented that FITS the PH format, useful and funny and don't look like I'm begging for subscribers. Kind of a win-win lead magnet.