The bug

It appears the page https://www.minecraft.net/en-us/demo is neither linked on the downloads page (https://www.minecraft.net/en-us/download/) nor from the "Trial & Download" entry in the burger menu (three horizontal lines, top right corner).

Additionally the downloads page (https://www.minecraft.net/en-us/download/) is misleading. It says "Free Trial", however nowhere else on the page is more information about that, instead the description even says the following which contradicts a "free trial":

You'll need to own Minecraft: Java Edition to play the full version. If you haven't bought it already go here and buy it quick!