The Apis bull is an actual real life bull, well, the concept is that they are a medium/incarnation of said gods, and when it dies, it rebirths into another bull. Alexander the Great when he freed egypt from Persian rule/religious prosecution, even went and paid his respects/gave sacrifices to, the Apis bull.
The head thing represents the sun (based on my understanding of egyptian mythology), and pretty sure like there was a specific holy religious man who was responsible for finding out who the Apis Bull reincarnated into when the previous one died.
So aesthetically, it's kind of just a bull, but within the mythology system, it's big d asf, worshipped as if it was a god itself.
https://www.ancient.eu/Apis/