An amiibo-compatible game can have either Read-only or Read/Write compatibility with an amiibo.
Read-only compatible means that you can tap an amiibo to the system’s NFC reader to get additional content. For example, the Mario amiibo figure will give you a special racing suit for your Mii™ character when used with the Mario Kart 8 Deluxe game.
Read/Write compatible, on the other hand, means that you can get additional content AND save certain game data to the amiibo. For example, you can customize your character and then save it to your Mario amiibo in Super Smash Bros. Ultimate. One amiibo can hold save data for one game at a time.
You can use an amiibo with save data on it in Read-only compatible games. That means you'll still get the additional content without having to use a different amiibo!