Google's feature that combines selected emoji into custom sticker-like designs is called Emoji Kitchen.
Emoji Kitchen was developed by Google and became available through Gboard, the company's keyboard application. Users select compatible emoji and receive generated combinations that can be sent as stickers or images.
The feature is different from Unicode emoji encoding. A Unicode emoji is text represented by a character or sequence, whereas many Emoji Kitchen results are image-based creations. They therefore do not necessarily behave like ordinary emoji when copied, searched, or read by assistive technology.
Google has expanded the library of combinations over time. Availability can depend on the keyboard, operating system, app, language, and regional rollout, so the same pair of emoji may not produce a result on every device.