This is also the approach I would have used - I was surprised the author didn't end up here. I used a separate VLAN to achieve same thing as author to shutdown internet access on the VLAN my kids devices use at bedtime, as well as another VLAN with no internet access at all for IoT devices, security cameras etc.

Blocking all UDP traffic by default is something I would never have even attempted for a domestic setup either. As the author discovers with Discord and Roblox, a great many common applications and games rely upon it. A UDP block on my kid's VLAN would last about 5 seconds before they attacked me for breaking their online Minecraft games.

The next(I think? It's in -CURRENT now anyway.) version of OpenBSD will be adding VLAN awareness to veb(4). Should make my OpenBSD home router experience much easier.