The short answer is that it doesn't. The iCloud website only shows devices that are actively uploading their location to Apple, such as iPhones and iPads. AirTags are not shown there, as they use the FindMy network instead (the whole other-devices-find-your-airtags mechanism). This library focuses on the latter.
Apple devices can query your AirTag's location because they sync its shared secrets through the iCloud keychain, which is used to generate temporary keys that can be use to download and decrypt the tag's location.
As far as I understand, the keychain is indeed e2e encrypted and it requires at least one of your other devices to be online in order to sync. However last time I checked Apple still fails the mud puddle test, so there does have to be some kind of master key that decrypts the data in the case of account recovery.
It’s explained pretty well in link provided in comment your replying to.
The tl;dr is: The information is publicly available in an encrypted form that is only readable by the party with the key.
Think of it like this, when you mark an item as lost you publish a hashed public identification key, if another device detects that key it creates a location report encrypted with your public key and posts it to a public list of encrypted reports, you decrypt the report with your private key.
If you mean from another device other than one that your keychain is on, ie, a browser on a device you haven’t logged into before, you can’t.
You can get an active location through iCloud if the device is powered on or its last location before power off if the setting is enabled. But you can’t decrypt find my location reports without the private key, which is only available in devices you’ve logged into.
So you're saying that by logging into icloud.com and clicking on the "Find My" app, my web browser is downloading encrypted location reports from Apple's servers, and my web browser is decrypting them locally?
