The focus is so strong on the app, that it assumes everyone owns a smartphone. The other day I saw a granny on the bus with a phone that was 2cms thick and predates the famous Nokia 3310. How is she and other users without a smartphone supposed to verify their age online?
How will this impact the browsing experience on the web? Every website has GDPR checkboxes these days which somewhat disrupts browsing experience if browsing in for example incognito mode. Imagine if you want to browse the web privately. Websites don't know who you are so you will have to verify your age every single time. This makes the web unusable for anyone who wants to browse the web privately. Especially on a pc. A solution would be to have some sort of browser extension that handles it automatically. Since you at least claim to value privacy that could work. But it wouldn't really look trustworthy. Note this doesn't only apply to incognito but browsing the web in general. Like trying to compare various news sites. Doing this for every website to visit is a major hindrance usability wise.