Yea that’s a nice UI feature. It’s basically what course sites use to mark a lesson as completed by the student.
That’s finsweet’s stuff and I was surprised to find they didn’t have this as a nice feature for you to drop into your Webflow site.
Maybe I’ve just missed it?
Based on your comment it sounds to me like you desire more of a plug-n-play solution.
If that’s the case, I’d strongly consider JetBoost’s favoriting feature: CMS Item Favoriting for Webflow | Jetboost
Even though it says “favoriting” on the tin, it’s the same thing as marking a lesson complete (checkout their demo).
Look at the features it gives you (screenshot above) most of which are exactly what you need to make this work out-of-the-box.