The upcoming "Nintendo Switch 2 Edition" version of Tears of the Kingdom introduces - among other things - a new feature that lets users share their Autobuild creations as QR codes.
QR coodes are used with the Nintendo Online mobile app.
During a Treehouse Live livestream, one of these QR codes was shown. This could be decoded to the URL https://s.nintendo.com/dd1/znca/game/5080866659500032?path=%2Ftotk%2Fschema-stones%2Ff17f67a7-31b2-428f-bac1-13d3a1641125%2Fadd.
The dd1 here indicates that this is on Nintendo's development/staging environment, so presubably this is the reason why the link 404's if you don't have access to this.
Unclear at this stage as to whether more information can be gleaned about Autobuild schema without requiring the app. Just wanted to document this for now so I can return to it.