Pi-hole v6 has an altogether redesigned REST-based API. Existing applications won't work without changes. You have already found the right place though - the app password is the new (way better!) way alternative to the API token.
Homepage dev here. I will take a look once I find the correct docs to read but quickly wanted to ask if there will be an easy way to detect api versions, or what the recommendation is? Iām certain we will have to support the old version for quite some time
The API itself is 100% documented using OpenAPI specs, and will be shipped with every Pi-hole offline. You may find an online copy here: Pi-hole API documentation
But the easiest way to see the interaction would probably be grabbing a v6 docker container and simply watch the Dev Tools in your browser while browsing the web interface.