The $25 one on the app store is probably the actual one. The creator of Anki has only monetized on iOS/iPadOS (one app, works on both) with a $25 one-time purchase. It's free on all other platforms it's available on (AnkiDroid is not his project, but is compatible and is also free), including on the web. His syncing service is free to use.

https://apps.apple.com/us/app/ankimobile-flashcards/id373493... <- the legitimate one

AnkiMobile is legit and is a $25 one-time purchase on iOS.

All other platforms are free, including AnkiWeb, which can be used on iDevices