FWIW It's done on the client side and there are multiple ways to bypass it.
https://news.ycombinator.com/item?id=46982421
https://tech.yahoo.com/social-media/articles/now-bypass-disc...
Things are changing quickly. Some users are being allowed only 3rd party age verification.
https://piunikaweb.com/2026/02/12/discord-uk-age-verificatio...
That K-ID bypass has already been patched, and even if it's bypassed again, Discord is apparently directing some users to Persona instead now. Persona does server-side classification so that one won't be as easy as nulling out the checks on the client.
The 3D model method might work on Persona, but that demo only shows it fooling K-IDs classifier.